Location,  Constraction 

and 

Maintenance  of  Roads 


GOODELL 


The  Location,  Construction 
and   Maintenance  of  Roads 


BY 

JOHN  M.  GOODELL 


Reprinted  from 

GOOD  ROADS  YEAR  BOOK 
1917 


NEW  YORK 

D.  VAN  NOSTRAND  COMPANY 

25  PARK  PLACE 

1918 


COPYBIGHT  1917 
BY 

AMERICAN  HIGHWAY  ASSOCIATION 

COPYRIGHT  1918 

BY 
D.  VAN  NOSTRAND  COMPANY 


COMPOSED  AND  PRINTED  AT  THE 

WAVERLY  PRESS 

BY  THB  WILLIAMS  &  WILKINS  COMPANT 

BALTIMOEE,  U.  S.  A. 


PREFACE 

In  the  summer  of  1916,  several  State  highway  engineers  re- 
ported to  the  American  Highway  Association  that  there  was 
need  of  a  concise  explanation  of  the  best  current  practice  in  locat- 
ing, constructing  and  maintaining  country  roads,  not  combined 
with  information  about  city  pavements.  It  was  found  by  these 
engineers  that  the  information  in  many  excellent  engineering 
treatises  proved  confusing  to  rural  road  officials  because  they 
did  not  have  sufficient  technical  knowledge  to  draw  a  line  be- 
tween what  was  applicable  to  country  highways  and  what  was 
restricted  to  urban  conditions.  Inquiry  showed  that  such  an 
outline  of  road-building  would  be  welcomed  by  the  road  officials 
of  other  States,  and  the  preparation  of  this  book  was  accordingly 
begun. 

Highway  engineers  in  all  parts  of  the  country  generously  con- 
tributed material  and  advice.  Special  attention  was  paid  to 
ascertaining  reasons  for  unusual  methods,  in  order  to  avoid  the 
publication  of  anything  useful  only  in  restricted  localities  and 
possibly  leading  to  trouble  if  tried  generally.  The  purpose  was 
to  furnish  information  of  a  national  value  rather  than  an  expres- 
sion of  the  views  of  a  few  individuals,  who  inevitably  have  per- 
sonal preferences  and  prejudices.  As  each  section  was  finished 
it  was  submitted  for  criticism  to  engineers  or  chemists  with 
special  knowledge  of  the  subjects  discussed,  and  most  of  the  chap- 
ters formed  by  combining  these  revised  sections  were  sent  out 
to  other  engineers  for  further  criticism.  Some  of  the  chapters 
were  revised  a  number  of  times  before  they  were  finally  ap- 
proved. As  a  consequence,  although  my  name  appears  as  the 
author  on  the  title  page,  the  book  is  rather  the  product  of  the 
cooperation  of  over  fifty  of  the  leading  American  highway  engi- 
neers and  the  patient  and  intelligent  handling  of  the  details  of 
the  work  by  Miss  Isabelle  Stockett,  at  the  time  chief  clerk  of  the 
American  Highway  Association. 

This  book  appeared  originally  as  Part  II  of  the  1917  Good 
Roads  Year  Book.  Its  wide  circulation,  the  many  references  to 
it  in  technical  journals,  and  its  use  as  a  textbook  by  engineering 
colleges,  indicating  that  the  volume  had  won  a  distinct  position 
in  technical  literature,  led  the  Directors  of  the  American  High- 
way Association  to  assign  the  copyright  to  the  D.  Van  Nostrand 
Company,  when  the  Association  was  dissolved  a  few  days  ago. 
By  this  action  the  results  of  the  cooperative  labors  of  so  many 
specialists  will  remain  available  to  the  public. 

iii 


IV  PREFACE 

Added  to  the  text  as  it  appeared  in  the  Good  Roads  Year 
Book  is  a  chapter  on  the  reasons  for  improving  roads.  This  is 
part  of  a  "good  roads  manual"  for  public  officials,  not  techni- 
cally educated,  which  had  considerable  circulation  in  manu- 
script form  among  road  commissioners  applying  to  the  American 
Highway  Association  for  such  information.  It  is  printed  here 
as  a  concise  justification  of  the  expenditure  of  public  funds  for 
road  improvements,  a  subject  which  highway  engineers  must 
frequently  discuss  at  public  meetings. 

JOHN  M.  GOODELL. 

Upper  Montclair,  N.  J.,  March,  1918. 


CONTENTS 

Location,  Grades,  Widths  and  Cross-Sections  of  Rural  Roads 1 

Regulations  of  the  California  Highway  Commission  Regarding  Surveys 

and  Plans 12 

Drainage,  Culverts  and  Bridges 19 

Earth  and  Sand-Clay  Roads 37 

Gravel  Roads 51 

Water-Bound  Macadam  Roads 64 

Road-Building  Rocks 75 

Concrete  Roads 90 

Standard  Specifications  for  Portland  Cement 107 

Petroleum  and  Residuums 109 

Asphalt  and  Native  Solid  Bitumens 117 

Asphaltic  Materials  for  Roads 124 

Tar  and  Tar  Products 132 

Bituminous  Roads 138 

Bituminous  Surface  Applications 150 

Brick  Roads 157 

A  Brick  Pavement  on  a  One-inch  Concrete  Base 178 

Highway  Bonds 180 

Resistance  of  Roads  to  Traction 189 

Rural  Public  Roads  in  the  United  States 192 

Money  Spent  on  Roads  in  the  United  States 193 

Extent  of  Surfaced  Roads  in  the  United  States 194 

Motor  Car  Statistics 195 

Vitrified  Paving  Brick  Production 196 

Broken  Stone  Production 198 

Gravel  and  Paving  Sand  Production 199 

The  Reasons  for  Improving  Roads 200 

Manufacturers  and  Constructors  Cards .  215 


LOCATION,  GRADES,  WIDTHS  AND   CROSS- 
SECTIONS  OF  RURAL  ROADS 

The  improvement  of  any  road  or  system  of  roads  must  begin 
with  a  study  of  its  location  and  grades,  for  unimproved  roads 
are  often  bad  in  both  respects.  The  purpose  of  relocation  is  to 
enable  the  road  to  carry  the  anticipated  traffic  with  the  least 
effort  and  loss  of  time.  It  is  impracticable  to  relocate  all  roads 
and  improve  their  grades  at  the  present  time,  and  highway  offi- 
cials must  be  satisfied  with  gradually  eliminating  or  at  least 
reducing  the  defective  conditions.  In  order  to  carry  on  this 
work  efficiently,  however,  the  entire  system  of  roads  under  a 
board  or  commission  must  be  studied  as  a  whole,  so  that  the 
whole  body  of  taxpayers  may  be  benefited  as  uniformly  as 
practicable  by  the  work  done  annually.  The  work  should  be 
planned  in  a  broad  way  several  years  in  advance,  if  possible,  for 
it  is  only  in  this  way  that  the  needs  of  all  parts  of  the  district  can 
be  met  without  favor  or  prejudice.  This  is  particularly  important 
where  the  needs  are  great,  the  road  funds  meager,  and  property 
has  been  developed  along  locations  where  roads  should  never  have 
been  laid  out.  The  situation  in  such  cases  has  been  summed  up 
as  follows  by  W.  S.  Keller,  State  highway  engineer  of  Alabama: 

The  genuine  bad  roads  cannot  be  maintained  for  the  reason  that  they 
have  never  been  constructed.  The  great  amount  of  work  necessary  to 
keep  them  in  passable  condition  disheartens  the  man  who  is  by  law  com- 
pelled to  work  them.  Until  these  roads  are  relocated,  avoiding  heavy  grades 
and  marshy  bottoms,  sharp  angles  and  useless  twists,  and  are  graded  so 
they  will  have  good  drainage,  we  may  expect  them  to  be  bad. 

Location. — It  is  evident  that  the  road  should  be  as  nearly 
straight  between  the  points  it  connects  as  the  configuration  of  the 
country  traversed  will  permit.  It  is  desirable,  however,  to  re- 
strict grades  to  6  per  cent  and  to  avoid  expensive  cuts,  fills 
and  bridges.  To  locate  the  road  properly  and  meet  all  local 
conditions  in  the  best  manner  requires  competent  engineering 
services;  if  they  are  not  obtained  there  is  a  strong  probability 
that  after  the  country  develops  new  locations  must  be  made  to 
meet  the  increased  transportation  needs  and  the  expenditures 
for  new  rights-of-way  will  be  far  greater  than  to-day.  But  if, 
for  the  present,  engineering  services  are  out  of  the  question,  the 
road  authorities  can  at  least  relocate  roads  that  are  plainly  un- 


;-•'•=.. 


2  AMERICAN  HIGHWAY  ASSOCIATION 

necessarily  low  and  marshy  and  unnecessarily  steep  and  high. 
This  is  particularly  the  case  where  roads  have  been  laid  out  on 
the  section  lines  of  the  government  land  surveys.  However 
desirable  the  rectangular  parceling  of  unoccupied  land  may 
have  been  in  attracting  settlers,  it  has  proved  a  heavy  handicap 
on  transportation  by  introducing  many  right-angle  turns  and 
causing  needless  length  in  the  roads  of  these  regions.  The  fol- 
lowing comment  on  this  condition  was  made  by  W.  S.  Gearhart, 
State  engineer  of  Kansas: 

A  60-foot  road  on  two  sides  of  a  section  of  land  occupies  14.55  acres, 
while  a  road  60  feet  wide  in  a  diagonal  direction  through  the  section  occu- 
pies 10.28  acres.  Thus  there  is  a  saving  in  the  diagonal  road  of  4.27  acres 
and  0.587  mile  of  distance.  The  saving  in  the  cost  of  right  of  way,  assum- 
ing that  the  land  along  the  section  line  is  as  valuable  as  on  the  diagonal 
line,  is  $85.40  if  the  land  is  worth  only  $20  per  acre.  This  amount  in  most 
cases  would  be  sufficient  to  grade  the  1.413  miles  of  diagonal  line  in  first- 
class  condition.  If  a  man  lives  4  miles  north  and  4  miles  east  of  his  market- 
place he  is  5.657  miles  on  the  diagonal  line  from  it;  that  is,  on  the  section- 
line  road  he  must  travel  4.686  miles  farther  in  making  the  round  trip  than 
on  the  diagonal  line. 

The  same  official  has  reported  that  a  county  commission  built 
a  mile  of  road  on  a  section  line,  which  crossed  the  same  stream 
three  times.  By  adopting  a  somewhat  different  location  and 
making  the  road  1J  miles  long,  the  stream  would  be  crossed  but 
once  and  the  road  become  of  greater  service  to  the  community. 
"More  than  $3,000  worth  of  steel  bridges  were  bought,  it  will 
cost  not  less  than  about  $2,500  for  the  abutments  to  set  these 
three  structures  on,  and  an  expenditure  of  $2,500  will  be  neces- 
sary to  make  the  road  passable,  or  a  total  of  about  $8,000  to 
accommodate  four  men  whose  property  is  reported  as  probably 
not  worth  as  much  as  the  cost  of  the  road."  Instances  of  this 
nature  prove  the  desirability  of  having  roads  located  by  engi- 
neers without  interference  from  political  or  personal  influences. 
The  assertion  that  such  services  are  unnecessary  in  connection 
with  such  relatively  inexpensive  highways  as  dirt  roads  is  best 
answereo!  by  pointing  to  the  action  of  the  Utah  State  road  com- 
mission in  substituting  an  entirely  new  location  about  15  miles 
long  for  an  old  route  in  Beaver  County.  This  was  done  by  the 
engineers  because  the  new  line  had  better  alignment,  grades  and 
road  materials. 

The  influence  of  soil  conditions  and  the  presence  or  absence  of 
road  materials  may  not  be  given  due  consideration  in  locations 
made  by  persons  who  are  not  engineers.  The  following  comments 
on  this  point  were  made  by  A.  N.  Johnson  in  a  report  on  the  high- 
ways of  Maryland: 


LOCATION  AND  GRADES  OF  RURAL  ROADS  3 

Should  it  happen  that  two  locations  are  possible  with  about  equal  ad- 
vantages and  disadvantages,  except  that  one  was  over  a  different  soil  from 
the  other,  that  location  should  be  taken  which  traverses  the  soil  best  cal- 
culated to  insure  a  good  road-bed.  For  example,  if  it  were  possible  to 
avoid  going  through  a  clay  section  when  a  more  open  soil  could  be  had 
close  at  hand,  much  would  be  saved  both  in  the  cost  of  construction  and 
in  the  subsequent  maintenance  by  going  over  the  more  open  soil.  It  is 
hardly  necessary  to  state  that  crossing  soft,  boggy  soil  should  be  avoided 
whenever  the  expense  of  going  around  such  a  place  would  be  no  more  than 
for  crossing  it.  If  possible  it  is  always  well  to  locate  a  road  in  the  vicin- 
ity of  good  road-material,  either  a  suitable  stone  or  gravel,  for  the  prox- 
imity of  such  material  lessens  for  all  time  the  cost  of  maintenance  of  the 
road,  and  when  this  point  is  considered  such  a  location  would  be  war- 
ranted even  at  an  increased  first  cost. 


PROFILE  OP  ROAD  IN  BALTIMORE  COUNTY,  MD. 

Showing  How  Relocation  Saved  a  Large  Sum  in  the  Improvement  of  the 

Road. 


Value  of  Engineering  Services. — Few  persons  realize  that  the 
expense  of  engineering  services  in  relocating  old  roads  is  gener- 
ally more  than  offset  by  the  saving  in  the  cost  of  construction 
of  a  properly  located  road  over  one  improperly  located.  The 
engineer  knows  how  to  fit  the  road  to  the  ground  in  hilly  country 
so  that  the  material  from  the  cuts  may  be  used  in  making  near- 
by embankments  and  costly  rock  excavation  will  be  reduced  to 
the  lowest  practicable  amount.  On  the  Maryland  State  high- 
ways, the  expense  of  moving  100  to  150  cubic  yards  of  earth  is 
from  $50  to  $75,  which  is  equal  to  the  cost  of  making  a  mile  of 
careful  surveys  that  may  be  reasonably  expected  to  save  more 
than  150  cubic  yards  of  such  earthwork.  The  accompanying 
illustration  shows  the  saving  in  excavation  expenses  on  a  road  in 
Baltimore  County,  Md.  The  hilly  character  of  the  old  road 
made  necessary  heavy  reductions  in  grade  to  give  a  highway  prop- 
erly accommodating  the  traffic.  The  heavy  cutting  to  give  suit- 


4  AMERICAN   HIGHWAY   ASSOCIATION 

able  grades  along  the  old  location  is  shown  by  the  diagram, 
while  the  light  excavation  and  filling  required  on  the  new  loca- 
tion is  also  indicated.  Such  savings  of  cost  can  only  be  made  by 
competent  engineers.  The  amount  of  detail  which  the  engineers' 
survey  must  furnish  depends  on  the  character  of  the  road  to  be 
built  and  the  nature  of  the  country.  Less  detail  is  necessary 
for  an  earth  road  in  a  flat  country  than  a  brick  road  in  a  hilly 
district,  for  example,  but  enough  should  be  obtained  to  make 
sure  that  the  final  location  is  along  the  line  on  which  the  cost  of 
transportation  plus  the  interest  on  the  first  cost  plus  the  cost  of 
maintenance  of  the  road  will  be  the  minimum  for  the  available 
funds  for  first  cost.  The  last  point  is  important,  for  the  best 
location  is  often  governed  by  the  amount  of  money  which  can 
be  spent  on  construction. 

In  carrying  out  extensive  work  by  contract,  experience  shows 
that  low  bids  from  responsible  contractors  are  best  secured  when 
full  information  is  obtained  for  their  use  in  preparing  estimates. 
For  instance,  in  carrying  out  road  improvements  in  Vermilion 
County,  Illinois,  under  a  $1,500,000  bond  issue,  about  1800  draw- 
ings of  plans,  profiles  and  cross-sections  were  prepared  in  the 
first  two  months  of  the  work.  These  were  plotted  on  Plate 
A  4  by  20  profile  paper  cut  into  32-inch  lengths.  The  longitu- 
dinal scale  of  the  plans  was  80  feet  to  1  inch  and  the  tranverse 
scale  40  feet  to  1  inch.  The  horizontal  scale  of  the  profiles  was 
80  feet  to  1  inch  and  the  vertical  scale  4  feet  to  1  inch.  The 
plans  show  all  section  corners,  bench  marks,  fence  lines,  shade 
trees,  farm  entrances,  property  owners'  names,  drains  and  cul- 
verts to  be  built,  and  any  other  data  necessary  for  a  complete 
knowledge  of  the  working  conditions.  The  cross-sections  are 
plotted  on  a  scale  of  4  feet  to  1  inch.  An  11  by  8J-inch  map  was 
made  of  the  location  of  14  sources  of  sand  and  gravel,  the  plants 
furnishing  paving  brick  and  the  railways  running  from  them  to 
the  district  where  the  roads  were  to  be  built,  and  24  by  20-inch  maps 
were  made  showing  the  roads,  railways  and  sidings  available  for 
contractors'  use.  The  existing  road  grades  were  shown  on  small 
maps,  and  other  small  maps  showed  the  location  and  size  of  pro- 
posed bridges  and  culverts. 

Grades. — The  effect  of  grades  on  hauling  is  usually  stated  in 
the  following  manner:  If  a  horse  can  pull  1,000  pounds  on  a 
level  road,  he  can  pull  810  pounds  with  the  same  effort  on  a  2 
per  cent  grade,  720  pounds  on  2f  per  cent  grades,  640  pounds  on 
3J  per  cent  grades,  540  pounds  on  4  per  cent  grades,  400  pounds 
on  5  per  cent  grades  and  only  250  pounds  on  10  per  cent  grades. 
These  figures  are  only  approximate  but  they  show  the  impor- 
tance of  reducing  grades  as  much  as  possible  where  traffic  is  heavy. 
Where  traffic  is  not  heavy,  the  cost  of  reducing  grades  below  3 


LOCATION  AND  GRADES  OF  RURAL  ROADS 


or  4  per  cent,  if  it  must  be  done  by  expensive  construction  or 
considerable  lengthening  of  the  road,  is  generally  considered  an 
unwarranted  expense. 

A  thoroughly  consolidated  roadbed  is  a  valuable  public  asset 
and  in  planning  grade  improvements  it  is  sometimes  undesirable 
to  cut  6  to  12  inches  into  such  a  road  for  a  long  distance  in  order 
to  secure  a  theoretically  perfect  profile. 

Where  a  road  will  probably  have  considerable  automobile 
traffic  the  grades  up  a  hill  should  be  flattened  somewhat  at  the 
top  if  necessary,  so  the  driver  can  see  an  approaching  car  when 
it  is  300  feet  from  him.  When  the  change  in  grade  at  the  sum- 
mit is  not  more  than  6|  per  cent,  no  flattening  is  necessary.  If 
the  change  is  10  per  cent  a  vertical  curve  about  200  feet  long 
should  be  employed;  for  a  13  per  cent  change,  a  curve  292  feet 
long  and  for  a  16  per  cent  change,  a  curve  360  feet  long. 

Widths. — Highway  commissions  in  many  parts  of  the  country 
are  reporting  that  their  roads  are  often  too  narrow  to  accommo- 
date the  traffic  coming  on  them  as  soon  as  they  are  improved. 
State  Highway  Commissioner  Everett  of  New  Hampshire  re- 
ports that  the  standard  width  of  21  feet  from  ditch  to  ditch 
is  not  wide  enough  on  many  of  the  roads  under  his  jurisdiction, 
and  the  experience  of  the  Wayne  County  road  commission,  in 
Michigan,  shows  that  the  minimum  width  of  hard-surface  road- 
way in  the  district  around  Detroit  should  be  16  feet  and  18  feet, 
and  should  be  adopted  wherever  practicable.  These  comments 
relate  to  double-width  roads.  A  width  of  8  feet,  previously  used 
for  single-width  roadways,  is  now  generally  considered  too  nar- 
row and  9  and  10  feet  are  advocated. 

Many  of  the  State  highway  departments  have  established 
standard  cross  sections  for  earth  roads.  The  present  standards 
in  Wisconsin  are  shown  in  the  diagrams  on  the  next  page.  They 
are  also  the  standards  for  macadam  and  gravel  roads  having 
a  hard  surface  9  feet  in  width.  Where  the  slopes  are  not  indicated 
they  are  made  in  accordance  with  the  accompanying  table. 
Guard  rails  are  used  when  the  vertical  distance  from  the  edge 
of  the  shoulder  to  the  top  of  the  ditch  is  more  than  4  feet. 

Slopes  Required  by  Wisconsin  Commission  in  Road  Work  in  Different 
Kinds  of  Soil 


SOIL 

ALL  CUTS 

FILLS  LESS  THAN 
FOUR  FEET 

FILLS  OVER  FOUR 
FEET 

Sand  and  sandy  gravel 

2    to  1 

3  to  1 

2    to  1 

Loam 

H  to  1 

3  to  1 

1$  to  1 

Clay  and  clay  gravels  
Hard  pan                       

1    tol 

5  to  1 

3  to  1 
3  to  1 

Utol 
1    to  1 

Solid  rock  

As  it  stands 

3  to  1 

As  it  stands 

AMERICAN   HIGHWAY   ASSOCIATION 


omourtt  of  vratev  HI 
drtchas  nil  I  b«  great  • 

cuton  intfrciC'f  ing  ditch 
of  top  OT  Mtn* 


Mot  3«ctK>n  in  Cuts  on  K  fit  to  moderotsly  heovy  3o«fa 


JitCh  beyona  toe  of  stone  rrnen 
ground  slopes  toward  till 


Section  on  fills  less  t nan  4 feet  above  •urroundmg  land 


—  .  NO-*  Section  on  Fills  more  tnon  A  teet  above  BO r rounding  lono 

"Dftcft  bvyond  toe  otMop« 
r»h«n  ground  Slope?  tovioitltUl 


ing  to 


Slope  occowfftg 
to  tools 


No 7  Section  for  side  hill  or  dug  out  AoadS 


STANDARD  EARTH  ROAD  SECTIONS,  WISCONSIN 


LOCATION  AND  GRADES  OF  RURAL  ROADS  7 

The  Wisconsin  sections  are  wide  enough  to  carry  a  16-foot 
roadway.  It  is  now  generally  held  that  the  distance  from  ditch 
to  ditch  should  be  24  feet,  even  for  a  single-width  road,  if  local 
conditions  permit.  In  some  States,  where  the  legal  right-of-way 
is  only  30  feet,  it  is  impracticable  to  secure  24  feet  between 
ditches  and  have  proper  fences  and  banks  along  the  road  where 
it  is  in  cuts.  It  is  necessary  to  obtain  extra  wide  rights-of-way 
in  such  cases  or  to  make  the  road  narrow. 

It  has  been  claimed  that  if  a  hard  surface  is  placed  on  a  road- 
bed, the  width  of  this  pavement  need  not  be  so  great  as  when 
the  traffic  is  carried  by  a  less  durable  surface,  and  consequently 
a  smaller  width  between  ditches  and  less  earthwork  are  required. 
This  argument  ignores  the  fact  that  a  narrow  roadway  concen- 
trates the  travel  and  may  cause  the  improved  surface  to  carry 
a  volume  of  traffic  for  which  it  is  unsuited.  For  this  reason  9 
and  10  feet  for  a  single-width  surfaced  roadway  and  16  or  18  feet 
for  a  double-width  roadway  are  generally  favored.  In  recent 
years  a  new  factor  has  become  important  in  determining  the  prop- 
er width  of  hard  surfacing.  Heavy  motor  trucks  and  omni- 
buses are  now  in  regular  service  on  many  roads.  If  they  turn 
off  a  hard  surface  on  to  a  soft  shoulder  they  may  become  mired 
or  unmanageable  and  crash  through  fences  or  guard  rails  before 
the  brakes  stop  them.  The  driver  is  usually  on  the  left  hand  of 
such  a  truck  where  he  cannot  easily  see  the  edge  of  the  hard 
paving,  and  consequently  he  keeps  his  truck  well  toward  the 
center  of  the  road  in  order  to  avoid  trouble  on  the  shoulders, 
although  the  driver  of  a  lighter  vehicle  would  keep  farther  over 
to  the  side. 

Where  the  road  is  used  by  carts  or  trucks  that  make  a  loaded 
trip  in  one  direction  only,  as  well  as  in  other  sections  where  funds 
are  not  available  at  present  for  a  double-width  paved  roadway, 
an  8  to  10-foot  pavement  has  been  laid  on  half  the  road,  with  one 
side  along  the  center  line,  as  though  a  similar  pavement  were 
to  be  laid  at  once  on  the  other  side  of  the  road. 

Rights-of-way. — The  width  of  the  road  is  restricted  in  the  older 
parts  of  the  country  by  narrow  rights-of-way,  which  are  trouble- 
some limitations  on  road  improvements.  Cuts  and  fills  of  more 
than  a  few  feet  widen  the  strip  occupied  by  the  road,  ditches  and 
side  slopes.  Telephone  poles  and  trees  along  the  road  require 
space,  and  provision  for  both  is  desirable.  As  a  result  of  long 
experience  in  Massachusetts  and  California,  reinforced  by  ob- 
servation in  many  other  States,  Austin  B.  Fletcher,  state  high- 
way engineer  of  California,  recommmends  securing  a  minimum  of 
50  feet  for  right-of-way,  and  60  feet  wherever  practicable. 

Acquiring  rights-of-way  is  an  annoying  feature  of  the  work  of 
highway  commissions,  and  in  any  extensive  undertaking  expe- 


8  AMERICAN    HIGHWAY    ASSOCIATION 

rience  shows  that  the  best  results  are  obtained  if  the  business  is 
handled  by  one  man,  with  whatever  assistance  is  needed.  Dip- 
lomatic methods  are  best  but  legal  warfare  is  sometimes  neces- 
sary, and  whatever  means  must  be  used  should  be  employed 
promptly  in  order  to  have  the  right-of-way  available  for  construc- 
tion as  soon  as  it  is  time  to  begin  work.  In  some  States,  it  is  un- 
necessary for  the  authorities  to  pay  for  private  property  taken 
for  public  use  in  advance  of  actually  taking  possession.  If 
the  property  owner  is  dissatisfied  with  the  original  offer  of  pay- 
ment or  the  award  made  to  him  by  the  public  authorities,  he 
may  pursue  his  remedy  in  the  appropriate  court,  even  though  his 
land  has  already  been  occupied  by  the  public.  In  other  States 
no  rights-of-way  can  be  taken  before  they  have  been  acquired, 
after  a  vast  amount  of  red  tape,  by  donation,  purchase  or  condem- 
nation. The  western  States  are  particularly  oppressed  by  such 
roundabout  methods  of  entering  upon  private  property  to  carry 
on  improvements  for  the  benefit  of  the  entire  community. 

It  has  been  Mr.  Fletcher's  experience  that  the  expense  of  ob- 
taining abstracts  of  title  to  ascertain  the  ownership  of  land  is 
unnecessary.  The  method  he  has  employed  in  securing  rights- 
of-way  for  hundreds  of  miles  of  California  highways  is  the  fol- 
lowing: When  the  field  parties  are  making  the  original  surveys, 
the  chiefs  of  party  usually  inquire  from  the  occupants  of  the  land 
surveyed  who  the  owners  or  those  interested  in  the  property  may 
be.  This  gives  a  clue  to  the  ownership.  Thereafter  one  of  the 
staff  visits  the  proper  county  officers  and  ascertains  from  the 
assessment  rolls  or  the  records  who  purport  to  be  the  owners. 
Deeds  or  agreements  are  then  prepared,  containing  the  proper 
descriptions,  and  it  is  very  rare,  indeed,  that  any  objection  has 
been  made  to  the  accuracy  of  the  instrument  submitted.  By 
thus  performing  its  own  title  searches,  even  though  thay  may 
not  have  always  been  the  most  exact  from  a  title  lawyer's  stand- 
point, the  authorities  have  saved  thousands  of  doUars  and  have 
never  had  an  injunction  or  ejectment  proceeding  instituted 
against  them  by  objecting  land  owners. 

Curves. — Sharp  curves  and  right-angle  intersections  are  danger 
places  where  vehicles  move  rapidly.  The  width  of  the  roads 
should  be  increased  on  sharp  curves,  except  where  it  is  already 
wide,  and  the  right-of-way  at  right  angle  intersections  should  be 
widened  and  cleared  so  as  to  give  drivers  on  the  crossing  roads 
a  good  view  of  approaching  vehicles.  This  is  not  always  prac- 
ticable, unfortunately,  but  road  commissions  should  keep  in 
mind  that  these  places  are  dangerous,  that  it  js  their  duty  to 
reduce  the  dangerous  conditions  on  the  roads  under  their  charge 
and  that  it  is  less  expensive  to  improve  these  places  now  than  it 
will  be  later. 


LOCATION  AND  GRADES  OF  RURAL  ROADS  9 

On  curves  on  a  road  with  a  uniform  cross-section  there  is  a 
tendency  for  the  drivers  of  motor  vehicles  to  stay  on  the  inside 
of  the  curves  because  the  centrifugal  effect  of  passing  on  the 
outside  is  unpleasant.  In  order  to  make  motor  travel  equally 
agreeable  on  any  part  of  the  cross-section  of  curving  roads,  it  is 
now  the  practice  to  superelevate  the  outside  of  the  road,  as  is 
done  on  railways.  Experiments  with  different  angles  of  super- 
elevation on  California  roads  have  led  the  highway  department 
of  that  State  to  adopt  a  slope  of  f-inch  rise  to  each  foot  of  width 
of  the  roadway  on  all  curves  having  radii  of  300  feet  or  less. 
The  transition  from  the  standard  crowned  cross-sections  to  the 
uniform  transverse  slope  stated  is  made  in  a  distance  of  about 
80  feet.  In  passing  from  the  straight  to  the  curved  road,  the 
outside  of  the  road  is  gradually  made  horizontal  and  then  grad- 
ually tipped  up  until  there  is  the  same  slope  throughout  the  sec- 
tion from  the  inside  to  the  outside  edge.  In  this  transition  the 
inside  edge  remains  at  the  same  elevation  it  would  have  if  the 
ordinary  crowned  cross-section  were  maintained;  the  change 
is  made  by  adding  to  the  height  of  the  other  parts  of  the  standard 
section,  so  the  improvement  is  generally  called  "banking  the 
curves." 

Grade  Crossings. — The  elimination  of  grade  crossings  is  a  prob- 
lem that  frequently  complicates  the  location  or  relocation  of 
highways.  The  usual  method  of  carrying  the  road  under  or  over 
the  railroad  tracks  is  so  costly  that  its  general  use  on  rural  roads 
is  impracticable.  Some  of  the  narrow  underpasses  with  sharply 
curving  approaches  that  have  been  built  on  roads  used  by  numer- 
ous automobiles  at  high  speed  are  almost  as  dangerous  as  the 
grade  crossings  they  replace.  Attention  is  therefore  being  given 
more  and  more  to  comprehensive  relocation  as  a  means  of  re- 
ducing the  number  of  grade  crossings  and  making  those  remain- 
ing less  dangerous  than  before.  For  example,  there  was  a  Wis- 
consin road  23.9  miles  long  with  16  grade  crossings  and  15 
such  crossings  on  branch  roads  feeding  it,  in  addition  to  3  under- 
passes and  2  overhead  bridges.  A  careful  study  by  the  State 
highway  commission  showed  that  by  reasonable  relocation  the 
total  number  of  crossings  could  be  reduced  to  16  at  grade,  4 
underpasses  and  2  overhead  bridges,  and  the  16  grade  crossings 
would  be  on  the  branch  roads,  none  remaining  on  the  main  road. 
The  total  cost  of  right-of-way  and  construction  for  such  an  im- 
provement was  estimated  at  $35,000,  much  less  than  the  cost  of 
elimination  in  the  usual  manner. 

The  New  York  State  highway  department  has  had  a  long 
experience  in  treating  grade-crossing  problems  and  as  a  result 
has  adopted  the  following  general  rules  for  location  at  such 
crossings : 


10  AMERICAN   HIGHWAY  ASSOCIATION 

1.  The  alignment  should  be  laid  out  so  that  approaches  are 
on  a  tangent  which  is  at  least  400  feet  long,  200  feet  on  each  side 
of  the  crossing.     The  angle  that  the  highway  makes  with  the 
railroad  should  not  be  less  than  60  degrees.     The  grade  of  the 
approaches  should  not  be  greater  than  6  per  cent,  and  there 
should  be  a  portion  level  or  nearly  so  for  a  distance  of  not  less 
than  100  feet  on  each  side  of  the  crossing. 

2.  On  the  highway  within  200  feet  of  the  railroad,  on  each 
side,  traffic  should  have  a  clear  view  of  approaching  trains  for  a 
distance  of  1,000  feet.     (See  Rule  5.) 

3.  The  width  of  the  planked  crossing  shall  not  be  less  than 
24  feet,  measured  at  right  angles  to  the  center  line  of  the  high- 
way.    The  ends  of  the  pavement  should  be  protected  by  an  edg- 
ing of  stone  or  concrete  placed  at  a  sufficient  distance  from  the 
ends  of  the  ties  to  allow  for  replacing  them. 

4.  A  standard  danger  sign  should  be  placed  at  each  side  of 
the  crossing  along  the  highway  in  a  prominent  location  at  least 
400  feet  from  the  crossing. 

5.  When  the  view  of  the  railroad  either  way,  as  required  in 
2,  is  less  than  1,000  feet,  or  when  there  is  a  great  deal  of  traffic 
on   either  the   highway   or   railroad,    or   when   vision   may    be 
blocked  by  cars  or  trains  as  in  the  case  of  a  railroad  with  two 
or  more  tracks,  a  flagman  should  be  employed  to  warn  highway 
traffic. 

The  New  York  State  highway  department's  rules  for  the  elim- 
ination of  grade  crossings  are  as  follows: 

1.  Subways  shall  have  a  clear  head-room  of  not  less  than  13 
feet  and  a  clear  width  between  abutments  of  not  less  than  26  feet. 
The  approaches  when  in  a  cut  shall  have  a  minimum  width  of 
28  feet  between  bottoms  of  slope.     When  a  highway  passes  over  a 
railroad  the  clear  height  over  said  railroad  shall  be  not  less  than 
21  feet  and  the  approaches  when  on  embankment  shall  be  not 
less  than  28  feet  wide  across  the  shoulders. 

2.  The  alignment  and  grade    of   approaches  shall    be    such 
that  traffic  at  any  point  within  the  limits  of  the  elimination 
will  be  able  to  see  that  approaching  it  for  a  distance  of  300  feet. 
The  maximum  allowable  grade  shall  be  6  per  cent. 

3.  Bridges   carrying   railroads   over  highways    shall  be  of  a 
solid-floor,   ballasted   type.     Drainage   of   such   floors   shall   be 
such  that  water  will  not  drop  upon  the  roadway.     Bridges  car- 
rying highways  over  railroads  shall  have  solid  concrete  floors 
with  a  minimum  width  of  roadway  of  18  feet. 

4.  When  an  elimination  is  made  on  a  highway  already  im- 
proved, the  pavement  shall  be  of  the  same  type  as  the  existing 
pavement.     If  the  highway  is  not  improved  the  pavement  shall 
be  the  same  as  that  contemplated. 


LOCATION  AND  GRADES  OF  RURAL  ROADS          11 

5.  Subways   shall   be   drained   in   a   thoroughly   satisfactory 
manner. 

6.  The  limits  of  an  elimination  shall  be  taken  as  the  points  of 
intersection  of  the  approach  grades  of  the  elimination  with  the 
grade  of  the  existing  highway. 


REGULATIONS  OF  THE  CALIFORNIA  HIGH- 
WAY COMMISSION  REGARDING 
SURVEYS  AND  PLANS1 

Part  1.    Surveys 

(a)  Note  Books. — Survey  note  books  will  be  furnished  to  the 
chief  of  party  by  the  Division  engineer.  No  survey  note  book 
other  than  the  standard  book  so  furnished  shall  be  used,  and 
the  use  of  loose  sheets  is  prohibited.  The  notes  placed  therein 
shall  be  the  "original"  notes  of  the  survey  and  shall  not  be  copied 
from  sheets  or  from  other  books. 

The  standard  book  shall  be  used  for  alignment,  topography 
and  levels,  and  for  all  other  information  which  the  survey  parties 
are  required  to  secure;  all  notes  shall  begin  at  the  bottom  of  the 
page  and  read  upward. 

On  beginning  a  survey  the  chief  of  party  shall  see  that  a  proper 
entry  of  the  Division,  county  and  route,  is  made  upon  the  label 
pasted  to  the  inside  of  the  front  cover  of  the  note  book. 

Attached  to  the  back  cover  of  each  book  are  several  pages 
showing  the  "standards"  required  in  all  surveys.  All  survey 
notes  shall  conform  in  so  far  as  possible  to  such  "standards"  to 
the  end  that  all  surveys  and  the  manner  of  taking  the  notes  thereof 
shall  be  uniform  throughout  the  work. 

At  the  beginning  of  each  day's  work  the  following  data  shall 
be  entered  in  the  book:  Date;  weather  conditions;  names  of 
members  of  party  and  duties  of  each. 

When  no  notes  are  taken  on  a  working  day  or  portion  of  a 
day,  the  date  shall  be  entered  and  the  reason  for  the  loss  of  time 
shall  be  stated  clearly  and  concisely. 

All  survey  and  other  notes  shall  be  suitably  indexed  on  the  first 
ruled  page  of  the  note  book. 

Every  day  at  the  close  of  the  work  the  notes  shall  be  copied 
neatly  upon  specially  printed  sheets  furnished  by  the  division 
engineer  and  numbered  consecutively,  and  after  careful  check- 
ing such  sheets  shall  be  forthwith  forwarded  to  the  division 
engineer. 

No  note  book  shall  contain  notes  relating  to  more  than  one 
route  or  to  more  than  one  county. 

1  From  Austin  B.  Fletcher,  State  Highway  Engineer  of  California. 

12 


REGULATIONS  OF  THE  CALIFORNIA  HIGHWAY  COMMISSION        13 

(b)  Alignment  Notes. — The  base  line  of  the  survey  shall  be 
referred  to  the  true  meridian,  which  shall  be  determined  by  ob- 
servation on  polaris.     The  chief  of  party  before  beginning  a  sur- 
vey shall  procure  all  tables  and  other  data  needed  for  such  deter- 
mination and  observations  shall  be  made  from  time  to  time  to 
ensure  the  accuracy  of  the  work.    The  line  shall  also  be  checked 
by  magnetic  bearings  taken  at  each  transit  point.     All  angles 
in  the  base  line  shall  be  azimuth  angles  read  from  the  back  sight 
and  repeated  with  the  telescope  reversed. 

Complete  traverses  shall  be  run  in  all  surveys  and  computed 
in  the  field.  If  the  error  of  closure  exceeds  1 : 5000  the  division 
engineer  shall  be  notified  and  the  party  shall  not  move  camp  until 
he  has  authorized  such  moving.  The  closures  shall  be  completed 
and  computed  in  such  lengths  as  the  division  engineer  shall 
prescribe. 

The  base  line  shall  be  as  nearly  as  may  be  in  the  center  of  the 
proposed  road.  When  it  is  apparent  that  a  tangent  base  line  will 
not  follow  the  approximate  center  of  the  proposed  road,  a  curve 
of  suitable  radius  shall  be  run.  Curves  shall  be  measured  by 
computing  the  length  of  the  arc  and  not  by  chords. 

If  the  survey  follows  an  existing  road,  wire  nails  not  less  than 
5?  inches  in  length  shall  be  driven  flush  with  the  traveled  way  at 
all  angle  points  in  the  base  line,  at  the  beginning  and  ending  of 
all  curves  and  on  long  tangents  at  intervals  not  exceeding  1000 
feet. 

When  the  base  line  does  not  follow  a  traveled  way  or  when  the 
roadway  is  so  soft  that  nails  will  not  hold  their  position,  wooden 
stakes  driven  flush  with  the  ground  shall  be  used  and  the  transit 
point  indicated  thereon  by  a  small  nail. 

All  transit  points  shall  be  properly  referenced  as  provided 
under  the  caption  "Stakes." 

Stations  shall  be  established  every  100  feet  on  the  base  line 
and  indicated  by  short  wire  nails  driven  through  bits  of  red 
cloth  into  the  ground  to  serve  as  temporary  markers  during  the 
survey.  The  stations  and  half  stations  shall  be  also  permanently 
marked  by  stakes  set  on  both  sides  of  the  proposed  road  suffi- 
ciently far  removed  from  the  base  line  to  prevent  their  being  dis- 
turbed during  the  building  of  the  road. 

(c)  Stakes. — All  stakes  which  are  to  be  used  for  establishing 
grades  shall  be  made  from  2x3  inch  scantling,  from  24  to  30 
inches  in  length,  laid  flat  and  sawed  diagonally  into  two  wedges, 
with  the  sharp  ends  approximately  J  inch  thick.    The  lumber 
from  which  the  stakes  are  made  shall  be  sound,  reasonably  free 
from  knots,  and  planed  on  all  sides.    These  stakes  shall  be  driven 
into  the  ground  to  about  one-half  of  their  length  with  the  2-inch 
face  parallel  to  the  base  line.    On  the  right  side  of  the  road  the 


14  AMERICAN   HIGHWAY   ASSOCIATION 

station  number  shall  be  marked  plainly  on  the  side  of  the  stake 
facing  Station  0,  and  on  the  opposite  side  of  this  stake  shall  be 
marked  to  the  nearest  tenth,  the  offset  from  the  base  line.  The 
face  toward  the  road  must  be  reserved  for  marking  during  con- 
struction. On  the  left  hand  side  of  the  road,  the  offset  from  the 
base  line  shall  be  marked  on  the  side  of  the  stake  facing  Station 
O  and  the  station  number  on  the  opposite  side. 

All  stakes  used  to  mark  monuments  and  for  transit  points  shall 
be  wedge  shaped,  not  less  than  1  foot  in  length  nor  less  than  f  x 
2-inch  at  the  top.  Such  stakes  shall  be  driven  flush  with  the 
ground  unless  they  are  so  located  as  not  to  endanger  the  travel- 
ing public.  Short  nails  driven  into  the  tops  of  these  stakes  shall 
indicate  the  monument  and  transit  points. 

All  monument  and  transit  points  shall  be  referenced  by  three 
ties  to  natural  objects  or,  if  such  do  not  exist,  to  stakes,  as  shown 
by  the  "standards"  at  the  back  of  the  note  book. 

(d)  Topography. — All  objects,  such  as  houses,  barns,  fences, 
gates,  field  entrances,  trees,  telephone  and  telegraph  poles,  power 
lines,  railroad  and  railway  tracks,  within  a  distance  of  150  feet 
on  either  side  of  the  base  line  shall  be  located  by  offsets  from  the 
base  line  and  recorded  in  considerable  detail,  and  the  limits  of 
the   "traveled  way"  on  all  existing  roads  shall  be  indicated. 
Separate  sketches,  with  levels  and  dimensions  of  all  essential 
features,  shall  be  made  in  the  note  book  of  all  bridges,  large  cul- 
verts and  other  appurtenances  of  the  road,  and  plainly  refer- 
enced in  the  topography  notes. 

The  azimuth  from  the  back  sight  to  the  boundary  lines  of  all 
incorporated  cities  and  of  all  counties  shall  be  ascertained  and 
recorded.  The  azimuth  of  the  boundary  lines  of  all  entering 
and  intersecting  highways,  of  township  lines,  and  of  division 
lines  between  property  holdings  shall  be  ascertained  and  re- 
corded with  reasonable  accuracy,  and  when  feasible  the  names 
of  the  owners  of  property  abutting  on  the  proposed  road  shall 
be  recorded. 

When  it  is  desirable  to  locate  topographic  features  from  a 
sub-tangent,  the  station  will  be  measured  from  the  nearest  end  of 
the  curve. 

(e)  Levels — Whenever  there   is  a   known   government  bench 
within  3  miles  of  the  survey,  the  datum  plane  of  such  bench  shall 
be  adopted  for  the  work.     If  no  such  bench  is  available,  a  datum 
plane  shall  be  assumed  at  such  an  elevation  as  will  be  low  for  all 
parts  of  the  survey. 

Benches  shall  be  established  during  the  progress  of  the  work 
at  each  end  of  the  survey,  at  city  and  county  lines,  and  at  other 
convenient  points  not  more  than  1000  feet  apart,  and  at  shorter 
intervals  on  grades. 


REGULATIONS  OF  THE  CALIFORNIA  HIGHWAY  COMMISSION        15 

Where  no  permanent  objects  or  structures  exist,  a  long,  sub- 
stantial stake  shall  be  driven  firmly  into  the  ground  and  prop- 
erly referenced. 

On  bench  marks,  at  turning  points,  and  on  construction  stakes, 
elevations  shall  be  determined  to  hundredths  of  a  foot. 

Cross  section  levels  shall  be  taken  to  tenths  of  a  foot  at  each 
100-foot  station  and  at  half  stations,  at  entering  and  intersecting 
roads,  for  not  less  than  200  feet  from  the  base  line,  at  driveways 
and  field  entrances  and  wherever  the  surface  of  the  ground  changes 
abruptly.  The  elevation  of  the  center  of  the  traveled  way  of 
an  existing  road  shall  be  taken  and  properly  noted  when  it  does 
not  coincide  with  the  base  line.  The  cross  sections  shall  include 
the  whole  width  between  fences,  and  where  the  grade  is  likely  to 
be  changed  substantially  the  cross  sections  shall  cover  a  width 
sufficient  to  include  all  ground  likely  to  be  affected. 

Sections  shall  be  taken  at  all  culverts  and  water  crossings,  and 
elevations  shall  be  taken  a  sufficient  distance  up  and  down  all 
streams  to  afford  data  for  designing  new  structures. 

(f)  General  Data. — The  survey  notes  shall  contain  data  con- 
cerning: 

1.  The  location  of  outcropping  boulders  and  bedrock,  suitable 
for  road  metal  or  concrete. 

2.  The  location  of  all  quarries  near  the  proposed  road. 

3.  The   location    and    approximate    quantity   of    field   stone 
available  in  the  vicinity  of  the  road. 

4.  The  location  of  all  gravel  pits. 

5.  The  location  of  points  where  good  river  sand  can  be  obtained. 

6.  The  available  points  where  water  for  sprinklers  and  steam 
rollers  can  be  obtained. 

7.  The  location  of  all  railroad  spur  tracks  or  sidings  within  rea- 
sonable haul  of  the  proposed  highway  and  the  name  of  the  railroad. 

8.  The  most  advantageous  locations  for  rock  crushing  plants 
along  the  road. 

9.  The  current  wages  paid  to  teamsters  and  laborers  in  the 
locations  through  which  the  road  will  pass.    Amount  paid  for 
hire  of  mules  or  horses  (without  driver)  per  day.     Amount  paid 
for  man  and  two-horse  team  per  day. 

10.  The   locations  where   special  underdrains   should  be   in- 
stalled due  to  the  existence  of  unstable  sub-soil  conditions.     In- 
quiry should  be  made  of  residents  and  local  officers  regarding 
spots  that  break  up  badly  in  wet  weather. 

11.  The  approximate  area  of  the  watershed  at  each  stream 
crossing  if  it  can  be  readily  obtained.    All  high-water  marks 
should  be  noted  and  inquiry  as  to  whether  or  not  water  over- 
flows the  road. 

12.  All  general  information  that  may  prove  of  value  in  the  con- 
struction of  the  highway. 


16  AMERICAN  HIGHWAY   ASSOCIATION 

Part  II.  Plans 

(a)  Drafting. — All  drafting  so  far  as  possible  shall  be  done  in 
the  division  offices.    At  the  Sacramento  headquarters,  the  draft- 
ing shall  be  limited  to  work  of  a  general  nature,  such  as  the  de- 
sign of  standards,  general  maps  and  to  such  revision  work  of 
the  plans  made  in  the  division  offices  as  may  be  necessary.    No 
drafting  shall  be  done  in  the  survey  party  camps  except  such  as 
'*s  immediately  needed  in  the  mountainous  country  to  facilitate 
il:^  choice  of  lines  and  grades. 

'!;•?•  plans,  profiles  and  cross-sections  shall  be  plotted  in  the 
division  offices  from  the  copies  of  the  survey  notes  sent  in  daily 
by  the  survey  parties  as  required  under  the  rules  for  surveys. 

(b)  Warkinn  Plans. — The  plan  and  profile  of  every  road  survey 
shall  be  plottt,  1  on  detail  paper  30  inches  in  width  and  of  such 
length  as  may  be  found  convenient,  the  plan  to  be  plotted  above 
the  profile,  and  such  drawings  shall  be  known  as  the  "Working 
Plans." 

Plans  and  profiles  shall  be  plotted  from  left  to  right,  the  plan 
on  the  scale  of  1  inch  to  100  feet  and  the  profile  to  the  same  hori- 
zontal scale  and  to  the  vertical  scale  of  1  inch  to  20  feet. 

The  base  line  of  the  survey  shall  be  plotted  by  coordinates 
obtained  from  the  traverse  sheets  which  have  been  made  and 
calculated  in  the  survey  camps  and  said  base  line  shall  be  inked 
in  red  before  the  topography  is  plotted.  All  angles  and  curve 
points  shall  be  marked  by  small  circles,  and  the  even  stations  by 
a  line  |  inch  in  length  drawn  at  right  angles  across  the  base  line. 

The  even  stations  and  the  plus  distance  of  all  angle  and  curve 
points  shall  be  numbered  below  the  base  line.  The  calculated 
bearings  of  the  base  line,  together  with  the  tangent  and  curve 
lengths  and  the  radii  of  the  curves,  shall  be  indicated  above  the 
line.  The  right-of-way  lines  shall  be  shown  hi  red.  They  shall 
be  properly  referenced  to  the  base  line  and  land  corners.  Where 
they  are  not  parallel  to  the  base  line  their  bearings  and  lengths 
shall  be  indicated.  The  topography  and  lettering  other  than 
that  relating  to  the  base  line  shall  be  done  neatly  and  so  as  to 
permit  of  tracing  easily  but  such  details  shall  not  be  inked. 

All  drafting  details  shall  conform  to  the  conventions  shown  on 
the  specimen  sheet  furnished  to  each  drafting  office. 

The  north  point  shall  be  indicated  at  intervals  of  not  more 
than  fifty  stations. 

The  datum  line  of  the  profile  shall  be  drawn  £  inch  from  the 
bottom  of  the  sheet  and  inked  in  black.  Perpendiculars  shall  be 
erected  at  each  even  station  and  inked  in  black.  The  even  sta- 
tions and  plus  distances  shall  be  numbered  below  the  datum  line 
and  the  elevations  of  the  present  surface  of  the  ground  shall  be 


REGULATIONS  OF  THE  CALIFORNIA  HIGHWAY  COMMISSION        17 

shown  above  the  datum  line  and  to  the  left  of  the  perpendiculars. 
The  elevations  of  the  proposed  finished  road  surface  shall  be 
shown  in  red  and  to  the  right  of  the  perpendiculars. 

The  present  ground  surface  shall  be  drawn  in  black,  and  the 
proposed  finished  surface  of  the  road  and  proposed  rates  per 
cent  of  grade  in  red.  Points  of  change  in  the  rate  of  the  finished 
grade  and  the  beginning  and  end  of  vertical  curves  shall  be  in- 
dicated by  small  circles. 

No  title  need  be  placed  on  the  working  plans;  they  shall  be 
identified  by  the  file  number,  and  such  plans  shall  bear  the  sig- 
natures of  the  employees  concerned  in  their  preparation  and  the 
date. 

(c)  Cross  Sections. — The  cross  sections  shall  be  plotted  to  the 
scale  of  1  inch  to  5  feet  vertical  and  horizontal  on  specially  ruled 
sheets,  20  by  30  inches  in  size,  furnished  by  the  highway  engi- 
neer.    They  shall  be  plotted  from  the  bottom  of  the  sheet  up- 
ward and  so  as  not  to  interfere  with  one  another  more  than  is 
necessary.     The  station  numbers  shall  be  placed  directly  below 
the  datum  line  and  across  the  base  line.    The  present  ground 
surface,  the  elevation  at  the  base  line  and  the  station  number 
shall  be  inked  in  black.     The  proposed  finished  surface,  together 
with  the  elevation  at  the  center  of  the  proposed  roadway,  shall 
be  shown  in  red. 

(d)  Layout  Plans. — The  layout  plans  shall  be  on  tracing  cloth 
20  by  30  inches  in  size  and  the  first  sheet  shall  carry  the  title, 
small  index  or  key  maps,  conventions,  and  the  necessary  certifi- 
cates and  signatures,  and  such  sheet  will  be  prepared  in  Sacra- 
mento.    The  subsequent  sheets  shall  be  traced  from  the  working 
plan,  shall  be  authenticated  by  the  signatures  of  the  division 
engineer  and  the  highway  engineer,  shall  state  the  whole  num- 
ber of  sheets  in  the  set  and  the  number  of  the  individual  sheet, 
the  file  number,  and  on  each  sheet  shall  be  shown  the  true  North 
Point.    These  plans  shall  conform  as  closely  as  is  practicable  in 
workmanship  and  appearance  to  the  specimen  sheet  hereinbefore 
referred  to. 

(e)  The  Grade  Line. — The  grade  shall  be  established  tenta- 
tively on  the  profile  under  the  direction  of  the  division  engineer 
and  transferred  to  the  cross-sections  and  the  proposed  finished 
surface  of  the  roadway  and  slopes  shall  be  drawn  on  the  sections 
with  the  aid  of  templets  to  be  furnished  by  the  highway  engineer. 
If  it  appears  to  be  desirable  to  shift  the  center  of  the  roadway 
from  the  base  line,  the  new  alignment  shall  be  located  on  the 
working  plan  by  a  dotted  redline.    The  limits  of  earth  work 
shall  be  shown  on  the  plan  by  a  dotted  red  line  where  they  ex- 
tend beyond  the  fences  or  known  right-of-way  lines. 

After  the  grade  line  has  been  so  tentatively  established  and 


18  AMERICAN   HIGHWAY   ASSOCIATION 

the  estimates  have  been  completed,  the  working  plan,  cross-sec- 
tions and  estimates,  together  with  sketches  of  special  structures, 
shall  be  submitted  to  the  highway  engineer  for  his  scrutiny. 

(f)  Accessions. — Every  plan  made  in  a  division  office  and  which 
is  to  remain  there  after  it  has  been  signed  by  the  division  engi- 
neer, shall  be  entered  in  the  "Accession  Book"  and  described  as 
required  by  the  captions  therein.    All  other  plans  and  maps  re- 
ceived at  such  offices,  and  which  are  to  remain  there,  shall  be 
likewise  entered  in  said  book. 

(g)  Filing  of  Plans  and  Note  Books. — All  plans  shall  be  filed 
flat  in  drawers  in  the  division  offices  but  during  their  prepara- 
tion the  working  plans  may  be  rolled  and  folded  afterward. 

When  completed,  the  layout  plans  shall  be  filed  at  Sacramento 
headquarters  and  on  the  completion  of  a  contract  the  cross- 
sections  shall  be  likewise  filed  at  Sacramento,  blue  prints  thereof 
being  furnished  to  the  division  offices. 

All  note  books  shall  be  filed  at  Sacramento  when  the  contract 
relating  to  the  surveys  therein  is  completed. 

All  documents,  whether  plans,  books  or  papers,  which  relate 
to  road  contracts  shall  be  stamped  with  the  file  mark  adopted. 


DRAINAGE,  CULVERTS  AND  BRIDGES' 

In  most  parts  of  the  country  water  is  one  of  the  most  destructive 
influences  on  roads.  When  it  collects  on  the  surface  it  tends  to 
inj  ure  the  roadway  unless  the  latter  is  paved  with  some  hard,  im- 
pervious material.  The  mudholes  on  earth,  gravel  and  broken 
stone  roads  become  soft,  so  that  traffic  increases  their  area  and 
depth  rapidly.  The  impervious  crust  is  finally  broken  through, 
allowing  water  to  reach  the  roadbed,  which  gives  way  under  heavy 
loads  and  the  condition  of  the  roadway  becomes  very  bad.  If 
water  collects  in  the  ditches,  it  percolates  sideways  into  the  road- 
bed, softening  it  and  eventually  causing  subsidence  which  produces 
marked  irregularities  in  the  surface,  so  that  mudholes  form  there. 
If  the  subgrade  on  which  the  roadbed  is  carried  is  soggy,  a  road 
can  not  be  maintained  on  it.  Charles  J.  Bennett,  State  highway 
commissioner  of  Connecticut,  has  reported  an  instance  of  this  in  a 
city  where  a  7-inch  broken  stone  roadway  was  placed  on  a  poorly 
drained  clay  subgrade.  The  roadway  broke  up  when  frost  came 
out  of  the  ground  and  became  so  impassable  that  stringers  were 
laid  on  it  and  covered  with  crossplank  to  furnish  a  driveway. 
This  heaving  action  of  frost  will  eventually  destroy  any  roadbed 
in  which  water  is  allowed  to  collect.  The  water  expands  every 
time  it  freezes.  The  expansion  opens  up  the  earth,  so  that  gradu- 
ally more  water  enters  it  and  finally  there  is  so  much  in  the  pores 
and  cracks  that  its  expansion  throws  up  the  roadway. 

Troubles  with  water  are  particularly  noticeable  on  grades.  The 
water  is  not  shed  so  quickly  from  the  roadway  on  steep  slopes  as 
it  is  on  fairly  level  roads,  but  runs  toward  the  side  ditches  at  an 
acute  angle  with  them.  If  there  is  any  check  to  the  flow  at  the 
side  of  the  roadway,  such  as  irregularities  of  the  surface  or  vege- 
tation offer,  some  scouring  will  eventually  take  place,  and  it  is  for 
this  reason  that  the  good  condition  of  the  shoulders  of  steep  roads 
is  important.  The  scouring  of  ditches  on  steep  grades  is  a  com- 
mon occurrence  after  heavy  rains,  and  experienced  maintenance 
men  regard  it  as  an  injury  that  must  be  repaired  immediately. 
If  the  road  is  on  a  fill  and  also  on  a  grade,  the  handling  of  water 
requires  special  care  if  heavy  gullying  of  the  slopes  is  to  be 
avoided.  A  gully  may  be  cut  a  quarter  of  the  way  across  a  new 

1  Revised  by  W.  F.  Childs,  Jr.,  Resident  Engineer,  Maryland  State  Roads 
Commission. 

19 


20  AMERICAN  HIGHWAY  ASSOCIATION 

road  in  such  a  location  by  a  single  heavy  rain.  An  unusual  case 
of  the  effect  of  water  on  slopes  has  been  mentioned  by  Mr.  Ben- 
nett. A  road  which  led  up  a  steep  hill  was  originally  only  wide 
enough  for  one  vehicle  and  was  the  drainage  channel  for  the  sur- 
face water  of  the  hillside.  The  surfacing  was  washed  away  by 
every  heavy  rain.  A  new  road  was  built  by  filling  in  stone  to  a 
depth  of  4  feet,  with  an  open  box  culvert  at  the  bottom  to  carry 
whatever  water  might  penetrate  beneath  the  road  from  the  sides. 
This  stone  fill  extended  the  entire  width  of  the  road,  from  shoulder 
to  shoulder,  and  very  deep,  wide  ditches  were  provided  at  each 
side.  There  has  been  no  trouble  with  this  road  since  it  was  re- 
constructed in  this  way,  showing  what  good  drainage  can  do  even 
in  an  exceptionally  bad  place. 

In  any  drainage  work  it  is  necessary  to  allow  for  the  different 
water-holding  capacities  of  different  materials.  Experiments  by 
the  United  States  Office  of  Public  Roads  and  Rural  Engineering 
show  that  with  the  same  condition  of  dryness,  clay  will  take  up 
more  water  than  sand,  but  will  not  part  with  so  much.  The  rate 
of  drainage  from  saturated  sand  is  almost  twice  as  fast  as  from 
saturated  clay  during  the  first  twenty-four  hours  after  the  mate- 
rials are  allowed  to  drain.  Silt  is  the  slowest  material  to  drain 
and  the  loams  come  between  sand  and  clay.  While  silt  and  clay 
absorb  more  water  than  sand,  they  allow  water  to  percolate  very 
slowly  indeed  in  comparison  with  sand,  and  it  is  for  this  reason 
that  they  form  water-tight  barriers  when  confined  so  their  grains 
can  not  flow  away.  When  in  a  loose  condition  silt  permits  the 
smallest  amount  of  percolation,  and  calling  the  rate  with  this 
material  1  the  rate  with  loose  clay  is  nearly  3,  loose  sandy  loam 
nearly  28  and  loose  sand  nearly  54.  With  compacted  materials, 
however,  such  as  exist  in  a  well-built  roadbed,  the  lowest  rate  of 
percolation  is  with  clay;  calling  it  1,  the  rate  with  compact  silt  is 
2,  compact  sandy  loam  15,  and  compact  sand  93.  The  experi- 
mental investigations  make  clear  the  reason  for  particularly  care- 
ful drainage  of  clay  and  silt  subgrades. 

General  Methods  of  Drainage 

Road  drainage  is  chiefly  a  matter  of,  first,  climate;  second, 
topography;  and  third,  soil.  It  may  be  treated  separately  under 
two  heads,  surface  draining  and  sub-surface  or  under-drainage. 

In  the  case  of  surface  drainage,  the  surface  water  may  be  shed 
in  four  ways,  first,  by  cross-slope  or  crown  in  construction;  sec- 
ond, by  longitudinal  grade  after  the  crown  is  determined;  third, 
by  discharge  into  natural  water-courses;  and  fourth,  by  discharge 
into  artificial  outlets. 

The  crown  should  be  determined  by,  first,  character  or  type  of 


DRAINAGE,    CULVERTS   AND   BRIDGES  21 

road;  second,  the  locality;  and  third,  by  grade.  The  crown  for  a 
natural  earth  road  or  a  shell  road  should  be  made  from  1  to  2 
inches  higher  in  construction  than  that  which  is  ultimately  de- 
sired. This  opinion  is  based  on  the  fact  that  these  types  of  roads 
are  more  susceptible  to  consolidation  and  displacement  under 
traffic  than  most  other  roads. 

In  thickly  populated  districts  a  high  crown  is  dangerous  to 
traffic  and  the  cross-slope  of  roads  constructed  through  towns  or 
other  thickly  populated  districts  should  be  reduced  to  that  which 
is  just  sufficient  to  shed  water  to  the  gutter  line.  In  such  dis- 
tricts high  crowns  cause  a  sliding  motion  of  vehicles  and  bring 
an  extra  strain  upon  lower  portion  of  the  wheels  which  is  objec- 
tionable and  causes  public  criticism,  which,  if  not  considered, 
brings  about  a  certain  amount  of  prejudice  against  modern  road 
construction.  Finally,  in  considering  crowning  of  roads  the  ques- 
tion of  grades  must  not  be  overlooked.  Ordinarily  the  practice 
is  to  increase  the  crown  as  the  grades  become  steeper.  For  all 
grades  up  to  and  including  5  per  cent,  the  crowns  mentioned  in 
the  next  paragraph  are  considered  sufficient.  When  the  grade  is 
in  excess  of  5  per  cent  the  crown  should  be  so  increased  that  the 
water  will  be  shed  to  the  side  of  road  rather  than  run  down  its 
surface  or,  at  least,  make  a  curve  in  its  course  of  final  dis- 
charge. 

The  minimum  and  maximum  crowns  which  it  is  desirable  to 
use  may  be  determined  by  multiplying  half  the  width  in  feet  of 
the  hard-surfaced  roadway  by  ^  to  1  inch  for  gravel  roads,  \  to 
f  inch  for  macadam,  J  to  \  inch  for  roads  with  a  bituminous  sur- 
face, and  \  to  f  inch  for  brick  and  concrete.  Formerly  curved 
cross-sections  were  used  with  impervious  pavements,  which  were 
quite  flat  at  the  center  and  increased  in  curvature  toward  the 
sides,  with  the  result  that  there  was  a  wholly  needless  slope  at  the 
latter.  This  has  been  changed  of  late,  and  there  is  a  tendency  to 
use  uniform  slopes  from  the  sides  toward  the  center,  where  an 
angle  is  avoided  by  introducing  a  very  flat  curve.  The  unpaved 
shoulders  are  often  given  a  slope  of  1  inch  per  foot  of  width. 

There  are  two  general  methods  of  draining  the  roadbed,  by  side 
ditches  and  by  underdrains,  which  will  be  explained  in  more  detail 
later.  In  flat  country,  the  roadbed  is  best  kept  dry  by  raising  it 
above  the  neighboring  land,  just  as  railway  roadbeds  are  raised. 
If  this  is  not  done,  it  is  very  difficult  to  keep  roads  in  good  condi- 
tion. 

In  undeveloped  swamp  country,  George  W.  Cooley,  State  en- 
gineer of  Minnesota,  has  found  the  most  permanent  roadbeds  can 
be  built  by  constructing  the  embankment  of  material  dredged  from 
a  drainage  ditch  on  the  upper  side  of  the  road  and  a  smaller  ditch 
on  the  lower  side.  When  the  swamps  have  soundings  of  2  to  5 


22  AMEKICAN    HIGHWAY    ASSOCIATION 

feet,  he  considers  that  the  elevation  of  the  bottom  of  the  dredged 
ditch  may  be  disregarded  except  that  it  should  not  be  above  the 
suitable  theoretical  grade  line.  This  is  because  the  surrounding 
land  is  swampy  at  all  times  and  the  subgrade  can  not  be  drained 
by  any  means  short  of  draining  the  whole  swamp. 

In  ordinary  flat  prairie  country,  the  elevations  recommended  by 
H.  E.  Bilger,  road  engineer  of  the  Illinois  highway  department, 
vary  with  the  kind  of  soil  used  in  the  roadbed,  as  follows:  with 
dense  clay  or  gumbo,  where  the  obtainable  grade  of  the  side  ditch 
is  less  than  0.4  per  cent,  not  more  than  800  feet  of  earth  road  in 
one  stretch  should  have  its  crown  less  than  12  inches  above  the 
adjacent  fields,  unless  the  road  is  along  a  ridge  or  on  a  side  hill  so 
that  culverts  will  deliver  the  water  from  the  uphill  ditch  to  nat- 
ural outlets  on  the  downhill  side.  In  partly  impervious  soils, 
such  as  loams,  the  same  elevation  should  be  maintained,  when 
the  side  ditches  have  a  slope  of  less  than  0.2  per  cent.  With  sand, 
gravel  or  very  loose  soil,  the  crown  should  be  6  inches  above  the 
adjacent  fields. 

It  is  troublesome  enough  to  care  for  the  surface  and  under- 
ground water  on  the  right-of-way,  without  having  the  work  ag- 
gravated by  water  from  adjacent  property.  On  hillsides,  there- 
fore, the  water  flowing  down  the  slopes  toward  the  road  is  often 
intercepted  by  ditches  along  the  crest  of  the  cuts,  as  shown  in 
Cross-Section  2  on  page  6,  and  carried  away  to  suitable  outlets. 
Such  ditches  are  sometimes  called  "berm  ditches."  In  sections 
where  irrigation  is  practiced,  considerable  trouble  is  sometimes 
experienced  as  a  result  of  the  overflowing  of  the  road,  and  to  pre- 
vent this  the  following  law  has  been  enacted  in  Colorado: 

No  person  or  persons  or  any  corporation  shall  cause  waste  water,  or  the 
water  from  any  ditch,  road  drain  or  flume,  or  other  place,  to  flow  in  or  upon 
any  road  or  highway  so  as  to  damage  the  same,  and  any  such  person,  or 
persons  or  corporation  so  offending  or  violating  any  of  the  provisions  of 
this  section  for  which  there  is  no  specific  penalty  provided  shall  pay  a  fine 
of  not  less  than  $10  nor  more  than  $300  for  each  offense,  and  a  like  fine  of 
$10  for  each  day  that  such  obstruction  shall  be  suffered  to  remain  in  said 
highway,  and  shall  also  be  liable  to  any  person,  or  persons  or  corporations 
in  a  civil  action  for  any  damages  resulting  therefrom;  and  it  shall  be  the 
duty  of  the  road  overseer  in  the  district  in  which  such  violation  shall  occur 
to  prosecute  any  person,  persons  or  corporation  or  corporations  violating 
the  provisions  of  this  act. 

The  water  accumulating  in  the  ditches  should  be  discharged  as 
quickly  as  possible  into  neighboring  outlets.  After  light  rainfalls, 
this  may  not  seem  important,  but  when  a  heavy  rain  occurs  in  the 
early  spring  while  the  roadway  is  impervious  the  need  of  numer- 
ous outlets  is  evident.  This  is  particularly  true  on  slopes,  where 
a  large  quantity  of  water  in  the  ditches  is  liable  to  scour  them 


DRAINAGE,    CULVERTS   AND    BRIDGES  23 

badly.  As  it  is  not  always  practicable  to  find  natural  drainage 
channels  on  each  side  of  the  road,  culverts  must  be  built  to  carry 
the  water  under  the  roadway  from  one  ditch  to  the  other,  as  well 
as  to  provide  adequate  channels  for  the  brooks  crossing  the  rights- 
of-way. 

Although  properly  designed  and  well-built  culverts  protect  a 
road-bed  from  injury,  it  is  sometimes  desirable  to  avoid  the  use 
of  large  structures  of  this  class  if  it  can  be  done  by  relocating  the 
road.  This  is  particularly  the  case  where  the  beds  of  the  streams 
are  in  alluvial  soil  which  is  readily  eroded  by  swiftly  moving  flood 
waters.  In  such  cases  there  is  uncertainty  whether  unpaved 
channels  to  and  from  the  culvert  will  not  become  so  eroded  that 
the  structure  will  settle.  Culverts  of  large  size  in  such  localities 
are  comparatively  expensive,  and  if  there  are  many  of  them  it  is 
always  well  to  ascertain  if  the  number  can  not  be  reduced  by  chang- 
ing the  position  of  the  road.  In  a  few  cases  winding  brooks  have 
had  straight  channels  dug  to  accomplish  the  same  purpose.  This 
is  particularly  the  case  in  districts  where  the  roads  follow  straight 
section  lines  without  regard  to  topography. 

The  most  elaborate  investigation  of  surface  and  underground 
roadbed  drainage  that  has  been  made  in  this  country  was  under- 
taken by  a  committee  of  the  American  Railway  Engineering  Asso- 
ciation, which  reached  the  following  conclusions: 

Side  ditches  should  be  provided  in  cuts,  whether  the  subgrade 
be  in  rock  or  earth.  The  minimum  side  ditch  should  be  1  foot 
wide  on  the  bottom  and  1  foot  deep  below  subgrade.  The  mini- 
mum grade  for  side  ditches  should  be  0.30  per  cent  If  the  rate 
of  grade  of  the  track  in  any  cut  is  less  than  0.30  per  cent,  the  cut 
may  be  widened  to  permit  side  ditches  to  be  constructed  on  0.30 
per  cent  grades,  or  drain  pipes  may  be  laid  to  proper  grades  below 
the  ditches  to  any  available  outlet. 

Efficient  subdrainage  of  wet  cuts  and  of  saturated  soil  upon 
which  embankments  rest  may  be  attained  by  the  use  of  pipe 
drains.  They  should  be  laid  immediately  below  the  center  of  the 
side  ditch  in  cuts  and  about  10  feet  from  the  toe  of  the  slopes  of 
embankments  and  on  grades  of  not  less  than  0.20  per  cent.  Care 
should  be  taken  to  locate  the  pipe  at  such  depths  that  no  dis- 
placement will  be  made  in  its  alignment  by  the  subsidence  of  the 
roadway  under  traffic.  To  this  end  the  trench  in  which  the  tile 
is  to  be  laid  should  be  dug  down  into  a  motionless  stratum  under- 
lying the  saturated  material  which  it  is  desired  to  drain.  The 
trench  above  the  pipe  should  be  completely  filled  with  cinders  or 
other  porous  material  which  filters  the  water  and  aids  its  passage 
to  the  pipe  and  prevents  the  intrusion  of  the  saturated  material 
under  pressure  of  traffic. 

A  water  pocket  beneath  the  track  may  be  drained  by  small 


24  AMERICAN   HIGHWAY  ASSOCIATION 

cross  drains  laid  in  cinder-filled  trenches,  or  by  trenches  filled 
with  cinders,  gravel  or  similar  material. 

The  committee  recommended  that  no  pipe  be  used  with  an  in- 
side diameter  of  less  than  6  inches,  except  for  cross  drains.  It 
will  rarely  be  necessary  to  use  larger  sizes  than  12  inches.  The 
trench  should  not  be  wider  than  is  needed  for  digging  it  economi- 
cally and  laying  the  pipe. 

Surface  intercepting  ditches  should  be  constructed  on  the  up- 
hill side  of  all  cuts  where  they  may  be  opened  without  causing 
slides.  Open  ditches  should  be  dug  along,  and  about  10  feet  from, 
the  toes  of  embankments  resting  on  soil  liable  to  become  unstable 
if  saturated,  to  divert  water  flowing  toward  the  embankment. 
Where  an  open  ditch  may  endanger  such  an  embankment,  a  drain 
pipe  may  be  laid  along  the  toe  of  its  slope.  In  constructing  ditches 
on  slopes  above  cuts,  they  should  not  be  larger  than  necessary  in 
order  that  they  may  not  become  the  notch  or  score  from  which  a 
slide  will  start.  They  should  be  10  to  25  feet  from  the  crest  of 
the  cut,  and  the  material  excavated  from  them  should  be  deposited 
on  the  side  nearer  the  roadbed. 

Side  Ditches 

The  cross-section  of  side  ditches  should  be  such  that  they  can 
be  formed  and  maintained  by  road  machines,  if  practicable,  for  the 
use  of  such  equipment  in  places  for  which  it  is  suitable  gives  the 
desired  results  at  lowest  cost.  The  sections  shown  on  page  226 
illustrate  the  capabilities  of  road  machines.  In  the  final  shaping 
of  the  road,  care  must  be  taken  not  to  dig  the  ditches  too  deep  at 
any  place,  leaving  a  depression  to  hold  water.  The  purpose  of  a 
ditch  is  to  carry  water  away  without  retaining  any  of  it.  If  any 
depressions  exist  they  must  be  remedied  in  some  effective  manner. 

Very  good  results  can  be  had  by  making  side  ditch  2  feet  wide 
on  the  bottom  with  a  4 : 1  slope  on  the  road  side  and  a  slope  on 
the  back  side  equal  to  the  angle  of  repose  of  the  particular  mate- 
rial encountered  in  the  excavation.  The  4:1  slope  on  the  road 
side  is  not  dangerous  to  traffic,  the  slopes  can  be  grassed  with  a 
good  texture  of  grass  and  the  slope  is  not  so  steep  as  to  become 
gullied  by  water  shed  into  the  ditch  from  the  surface  of  the  road 
where  the  crown  is  excessive  or  the  grade  steep.  The  slopes  can 
also  be  made  and  maintained  with  a  road  machine. 

The  grade  of  the  flow-line  of  the  ditch  should  be  0.5  per  cent  if 
possible,  rather  more  than  the  recommendation  for  railway  ditches 
previously  quoted,  but  in  flat  country  it  is  sometimes  impracticable 
to  secure  such  a  grade.  Under  such  conditions  the  grade  lines  for 
the  ditches  should  be  given  by  a  surveyor,  and  the  excavation 
made  to  conform  exactly  to  the  lines.  When  finished,  these  flat 


DRAINAGE,    CULVERTS   AND   BRIDGES  25 

ditches  must  be  maintained  on  the  true  grades,  or  water  will  fail 
to  run  off  quickly.  Flat  ditches  are  often  made  wide  and  shallow, 
so  as  to  expose  as  much  water  to  evaporaton  as  possible,  and  on 
well-maintained  level  roads  care  is  taken  that  these  shallow  ditches 
are  not  unduly  shaded  by  trees  and  shrubs,  so  that  evaporation 
will  be  checked. 

Where  there  are  two  convenient  outlets  with  a  side  ditch  run- 
ning from  one  to  the  other,  the  grade  may  be  improved  and  a 
deep,  unsightly  ditch  avoided  by  selecting  a  good  intermediate 
summit  and  drawing  water  both  ways  to  the  outlet.  This  summit 
may  be  regulated  by  the  grades  desired  or  by  holding  them  from 
6  to  12  inches  below  the  sub-grade  at  the  summit  and  running 
straight  flow-line  grades  each  way  to  the  outlets. 

Deep,  narrow  ditches  with  steep  sides  have  two  defects  fre- 
quently observed  where  roads  are  not  maintained  properly.  One 
defect  is  the  danger  they  offer  to  vehicles  which  may  be  crowded 
into  them  for  any  reason.  The  records  of  the  Iowa  State  high- 
way commission  for  September,  October  and  November,  1916, 
show  that  in  that  State  alone  353  automobiles  turned  turtle,  re- 
sulting in  5  deaths  and  451  injuries.  Just  how  many  of  these  ac- 
cidents were  due  to  ditching  the  cars  is  not  stated,  but  this  is  gen- 
erally regarded  as  the  usual  cause  of  overturning.  Where  the 
ditches  are  deep  or  the  road  is  on  an  embankment  with  steep 
slopes,  substantial  guard  rails  should  be  provided.  During  Sep- 
tember, October  and  November,  1916,  the  Iowa  records  show  that 
167  cars  went  over  embankments,  killing  7  persons  and  injuring 
234.  Such  a  list  points  more  clearly  than  general  arguments  to 
the  great  importance  of  guard  rails  that  will  act  as  real  guards. 

The  second  defect  is  the  relatively  high  velocity  which  water 
may  acquire  in  a  deep,  narrow  ditch.  If  the  latter  is  protected 
against  erosion  high  velocity  may  cause  no  trouble,  but  such  pro- 
tection is  not  common  and  when  the  water  rushes  through  an 
earth  ditch  the  latter  will  become  eroded  and  both  the  roadbed 
and  the  bank  may  be  severely  injured. 

The  maintenance  of  ditches  cut  in  earth  on  slopes  is  hardly 
possible  unless  water-brakes  are  constructed  in  them.  These 
are  usually  heavy  timbers  placed  across  the  ditch  and  projecting 
several  inches  above  it.  They  check  the  flow  of  the  water  at 
intervals  down  the  hill,  and  thus  prevent  a  velocity  which  will 
be  destructive.  The  ditches  where  they  are  used  must  be  cleaned 
out  after  every  rain  or  the  bottoms  will  become  filled  to  the  top 
of  the  timbers  and  later  storms  will  gully  the  road  and  the  banks 
at  their  ends.  In  some  cases,  the  water-brakes  are  heavy  con- 
crete beams.  Where  the  water  attains  an  erosive  velocity  in 
ditches  paving  protects  them  better  than  the  waterbrakes. 

Wherever  practicable  ditches  in  earth  on  grades  exceeding 


26  AMERICAN   HIGHWAY   ASSOCIATION 

5  per  cent  should  be  paved.  This  adds  somewhat  to  the  first 
cost,  even  when  field  stone  suitable  for  the  purpose  can  be  ob- 
tained in  the  vicinity,  but  the  first  cost  is  offset  by  the  reduced 
expense  for  maintenance. 

The  outlets  from  the  ditches  should  receive  careful  attention, 
because  they  are  frequently  a  source  of  needless  expense  for 
maintenance.  There  should  be  a  paved  channel  of  sufficient  size 
leading  from  the  ditch  to  the  waterway  into  which  the  water 
is  discharged.  If  field  stone  for  such  a  pavement  can  not  be 
obtained,  it  will  be  advisable  to  employ  concrete. 

The  protection  of  the  embankments  by  grass  or  other  vege- 
tation is  a  remedy  for  scouring  used  on  many  railways  and 
some  highways.  Witch  grass  is  a  good  species  for  the  purpose,  but 
must  not  be  used  near  cultivated  land.  Bermuda  grass  and  red 
top  have  been  recommended  for  some  localities  and  other  varie- 
ties are  probably  better  suited  for  different  local  conditions. 
On  the  Southern  Railway  the  banks  have  been  held  by  planting 
the  volunteer  or  Japanese  honeysuckle  in  parallel  horizontal 
rows  about  10  feet  up  the  slopes.  Where  the  slopes  stand  satis- 
factorily except  during  heavy  rains,  and  the  material  is  such  that 
vegetation  will  not  grow  on  them,  they  are  sometimes  held  in 
place  by  covering  them  with  coarse  cinders  and  gravel.  This 
prevents  the  water  from  coursing  down  them  unchecked  and 
thus  checks  erosion. 

At  every  driveway  from  a  road  into  adjoining  property,  there 
is  likely  to  be  an  obstruction  of  the  ditch  crossed  by  this  drive. 
If  the  ditch  is  shallow  with  gently  sloping  sides,  the  best  drive 
from  a  drainage  viewpoint  is  a  paved  strip  from  the  roadway 
across  the  ditch  into  the  property.  Unfortunately  this  is  not 
often  practicable  and  rarely  adopted  when  it  is.  The  usual 
driveway  is  formed  by  filling  dirt  over  a  flimsy  plank  drain  or 
a  line  of  4-inch  tile  on  an  insecure  foundation,  and  this  affords 
wholly  inadequate  drainage.  A  culvert  with  an  ample  water- 
way should  be  provided,  with  a  substantial  facing  or  headwall 
at  each  end.  Sometimes  culverts  under  driveways  can  be  omitted 
in  the  case  of  shallow  side  ditches,  by  locating  a  summit  at  the 
entrance  and  running  the  grade  down  in  both  directions  from  it  to 
well-defined  outlets. 

At  such  drives  attention  should  be  paid  to  the  amount  of 
water  they  may  discharge  into  the  side  ditches.  Sometimes  on 
a  hillside  a  driveway  will  discharge  a  large  volume  of  water  at 
such  a  high  velocity  that,  unless  properly  led  away,  part  of  it 
will  flow  across  the  road  to  the  other  side,  which  does  the 
shoulders  and  roadway  no  good  and  may  cause  serious  injury. 


DRAINAGE,    CULVERTS   AND    BRIDGES  27 

Underdrainage 

The  usual  method  of  repairing  a  wet  place  adopted  by  an 
untrained  roadbuilder  is  to  dump  stone  over  it.  After  the  stone 
has  been  forced  into  the  mud  by  the  traffic,  more  stone  is  dumped 
there,  with  the  result  that  a  mudhole  is  formed  at  each  end  of 
the  stone  fill.  The  water  is  in  the  earth  and  must  find  an  outlet 
somewhere.  Instead  of  trying  to  seal  it  up,  the  proper  remedy 
is  to  carry  it  off  by  some  kind  of  underdrainage.  The  problem 
of  caring  for  underground  water  is,  first,  a  matter  of  soils ;  second, 
a  matter  of  topography;  and  third,  one  of  temperature.  There 
are  many  soils  of  a  gravelly,  sandy,  or  similar  character,  which 
ordinarily  are  self-draining  to  a  degree  and  do  not  require  par- 
ticular attention.  The  difficulty  is  with  those  highways  built  on 
clayey  or  loamy  soils  which  are  more  or  less  retentive  and  do  not 
drain  readily. 

When  the  entire  roadbed  is  somewhat  damp  or  soggy  it  was 
formerly  the  general  practice  to  lay  a  foundation  of  large  stones 
wedged  together  by  small  stones  and  thoroughly  rammed.  This 
is  called  a  Telford  foundation  and  is  6  inches  or  more  thick. 
It  is  still  used  extensively  for  the  purpose  but  there  are  sub- 
stitutes for  it  which  have  come  into  use.  In  some  cases  from 
6  to  12  inches  of  coarse  gravel  or  small  field  stone  are  placed 
on  the  subgrade  and  rolled.  Still  another  type  of  drainage  foun- 
dation, developed  first  in  Massachusetts,  is  formed  by  excavating 
the  subgrade  to  a  V-shape  cross-section,  6  to  8  inches  deep 
at  the  sides  and  12  to  18  inches  deep  at  the  center,  and 
filling  this  with  field  stones,  the  largest  at  the  bottom.  With 
any  of  these  types,  there  should  be  an  outlet  every  50  feet  or  so 
from  the  lowest  part  of  the  foundation,  formed  by  cutting  a 
trench  through  the  shoulders  to  the  side  ditches  and  backfilling 
it  with  coarse  gravel  or  stone.  Even  when  the  road  is  not  on 
wet  land,  many  engineers  build  cross  drains  filled  with  stones  at 
50-foot  intervals  in  the  top  of  the  subgrade  of  gravel  and  mac- 
adam roads.  They  are  5  or  6  inches  deep  at  the  center  and 
are  at  right  angles  to  the  ditches  except  on  hills,  where  they  in- 
cline slightly  downhill  from  the  center. 

In  many  parts  of  the  country  stone  or  gravel  is  unavailable 
for  such  drainage  work  and  drain  tile  has  been  employed.  It 
has  proved  successful  and  economical,  even  when  stone  could  be 
obtained,  provided  it  was  laid  properly.  Many  engineers  recom- 
mend using  drains  whenever  water  remains  in  the  ground  for  a 
considerable  period  of  time  within  3  feet  of  the  surface.  The 
reason  for  this  is  that  the  maintenance  of  a  well-drained  road 
is  easier  work  than  if  the  subgrade  is  soggy.  If  a  heavy  rainfall 
soaks  the  top  of  a  road  which  is  already  soft  below  the  surface, 


28  AMERICAN   HIGHWAY   ASSOCIATION 

heavy  loads  are  liable  to  rut  it  seriously,  because  it  will  take  much 
longer  to  dry  out  than  a  well  underdrained  road.  In  the  early 
spring,  when  the  water  in  the  ground  freezes  and  thaws  alter- 
nately, good  underdrainage  is  particularly  useful  in  preventing 
the  upheaval  of  parts  of  the  road. 

The  influence  of  a  well-laid  line  of  drain  tile  upon  the  position 
of  the  upper  surface  of  the  ground-water,  called  the  "water  table" 
by  many  engineers,  is  greater  than  many  persons  realize.  Prof. 
Ira  O.  Baker  has  reported  the  following  experimental  proof 
of  the  extent  of  this  influence.  Lines  of  drain  tile  were  laid 
50  feet  apart  and  2J  feet  deep  in  a  field  notoriously  soggy 
and  heavy  on  account  of  the  presence  of  hardpan  which  held 
the  water  "like  a  jug."  Where  the  field  was  without  drainage 
the  water  rose  to  within  6  inches  of  the  surface.  Where  it 
was  drained,  the  water  level  midway  between  the  drains  was 
18  inches  below  the  surface,  showing  that  even  in  such 
very  heavy  soil,  the  top  surface  of  the  ground-water  25  feet 
from  the  drain  was  only  1  foot  above  the  tile.  It  is  this  wide 
influence  of  good  drains  which  makes  the  effect  of  a  single  line  of 
deep-laid  tile  along  one  side  of  a  road  greater  than  that  of  shal- 
low lines  along  both  sides.  The  general  rule  of  agricultural 
drainage  experts  is  to  place  drains  100  feet  apart  and  at  a  depth 
of  3|  to  4  feet. 

The  drain  is  best  laid  in  a  trench  below  the  ditch  at  the  side 
of  the  road  from  which  the  greatest  amount  of  ground-water  is 
expected.  Although  a  large  number  of  drains  laid  perfectly 
horizontal  for  long  distances  have  given  satisfactory  service,  it  is 
desirable  to  give  them  a  uniform  slope  of  at  least  2  inches  per 
100  feet  if  possible.  This  is  a  somewhat  lower  minimum  grade 
than  some  engineering  books  recommend,  but  is  warranted  by 
experience.  The  tile  should  not  be  smaller  than  4-inch,  and  if 
the  ground  contains  a  large  amount  of  water  and  the  outlets 
of  the  drains  are  far  apart,  larger  sizes  may  be  desirable,  partic- 
ularly in  level  country. 

Tile  should  not  be  laid  except  from  grade  lines  given  by  the 
engineer,  and  they  must  be  laid  accurately  to  line  and  grade. 
The  trench  to  receive  them  should  be  no  larger  than  is  necessary 
to  lay  them  properly  at  the  least  expense,  but  in  opening  a  trench 
it  is  sometimes  less  expensive  to  make  it  wider  than  required  for 
the  tile,  because  of  the  extra  cost  of  digging  in  a  very  narrow 
trench.  In  any  case  the  bottom  should  be  cut  very  carefully 
so  as  to  have  it  exactly  on  the  right  grade.  If  there  is  any  prob- 
ability that  the  bottom  will  settle  and  throw  the  tile  out  of  align- 
ment, a  4  by  1-inch  plank  is  sometimes  laid  to  support  the 
tile.  The  ends  of  the  tile  are  laid  touching.  Some  engineers 
recommend  covering  the  top  half  of  the  joint  with  tar  paper  or 


DRAINAGE,    CULVERTS   AND   BRIDGES  29 

burlap,  but  this  is  probably  unnecessary  if  the  trench  is  back- 
filled with  clean  gravel  or  broken  stone  from  1  to  4  inches 
in  size,  which  is  the  best  material  to  use.  In  any  case  the  fill- 
ing should  be  porous  and  placed  carefully  so  as  not  to  move  the 
tile.  When  the  gravel  or  stone  filling  is  within  12  inches  of 
the  surface,  some  engineers  coyer  it  with  about  3  inches  of 
hay  or  straw  before  the  earth  filling  is  placed  to  form  the  bottom 
of  the  side  ditch. 

The  outlets  of  the  drains  should  be  constructed  with  special 
care,  because  they  are  particularly  liable  to  injury.  They  are 
preferably  made  of  stronger  pipe  than  agricultural  tile,  firmly 
supported  and  protected  at  the  end  by  a  substantial  wall  or 
facing.  A  drain  with  its  end  stopped  is  of  little  value. 

Pipe  drains  are  the  most  serviceable  type,  but  there  are  vari- 
ous substitutes.  One  of  these  is  a  covered  trough  of  rough  stone, 
another  is  a  similar  plank  trough,  and  another  is  merely  a  mass 
of  gravel  and  stones,  with  the  largest  pieces  at  the  bottom.  The 
drawback  of  all  of  these  is  that  they  tend  to  break  down  or  be- 
come clogged  with  fine  material,  which  can  not  enter  a  properly 
laid  tile  drain. 

Where  the  side  ditches  are  on  very  flat  grades,  they  are  some- 
times drained  into  the  underdrains  at  intervals  of  about  0.1  mile 
by  blind  catch-basins.  These  are  merely  masses  of  coarse  gravel, 
stone  or  brickbats  reaching  from  the  bottom  of  the  ditch  to  the 
tile,  and  covered  at  the  top  by  a  low  pile  of  similar  material 
which  acts  as  a  screen.  By  this  means  the  side  ditches  need 
not  be  cut  so  deep  as  to  be  dangerous.  Where  the  side  ditches 
carry  large  quantities  of  water  which  must  be  drained  off  in  this 
manner,  large  drain  tiles  are  needed  and  open  brick  or  concrete 
inlets  like  those  used  on  sewerage  systems  may  be  used. 

Where  an  embankment  is  built  on  a  wet  side  hill,  the  latter 
must  first  be  underdrained  thoroughly  to  prevent  slipping  of  the 
embankment.  When  an  embankment  in  such  a  locality  begins 
to  slip,  the  trouble  may  sometimes  be  remedied  by  digging  large, 
deep  intercepting  ditches  on  the  high  side,  leading  to  the  nearest 
culverts.  These  ditches  are  usually  filled  with  stone.  Any 
pockets  in  the  ground  near  the  uphill  toe  of  the  embankment,  in 
which  water  may  collect  and  soften  the  neighboring  earth  or  clay, 
should  be  filled. 

Size  of  Culvert  Openings  and  Bridge  Waterways 

The  waterway  to  be  provided  for  large  culverts  and  bridge 
openings  depends  upon  many  conditions,  which  have  been  stated 
as  follows  by  Prof.  A.  N.  Talbot: 


30  AMERICAN  HIGHWAY  ASSOCIATION 

1.  The  variation  of  the  rainfall  in  different  localities. 

2.  The  meagreness  of  rainfall  data,  since  records  are  gener- 
ally given  as  so  much  per  day  and  rarely  per  hour,  while  the  du- 
ration of  the  severe  storms  is  not  recorded. 

3.  The  melting  of  snow  with  a  heavy  rain. 

4.  The  permeability  of  the  surface  of  the  ground,  depending 
upon  the  kind  of  soil,  condition  of  vegetation  and  cultivation,  etc. 

5.  The  degree  of  saturation  of  the  ground  and  the  amount 
of  evaporation. 

6.  The  character  and  inclination  of  the  surface  to  the  point 
where  the  water  accumulates  in  the  watercourse  proper. 

7.  The  inclination  or  slope  of  the  watercourse  to  the  point 
considered. 

8.  The  shape  of  the  area  drained  and  the  position  of  the 
feeders. 

The  importance  of  this  item  will  be  seen  in  comparing  a  spoon- 
shaped  area  where  the  main  watercourse  is  fed  by  branches  from 
both  sides  so  arranged  that  water  from  the  whole  area  reaches  the 
culvert  at  the  same  time,  with  a  long,  narrow  basin  in  which, 
before  the  water  from  the  upper  part  reaches  the  opening,  the 
rainfall  from  the  lower  portion  has  been  carried  away  and  the 
severe  part  of  the  storm  is  past. 

While  there  are  three  formulas  giving  the  size  of  waterways 
for  drainage  areas  of  different  sizes,  it  is  generally  agreed  by 
engineers  that  it  is  best  to  find  out  by  examination  and  inquiry 
if  possible  the  flood  heights  of  any  stream  that  is  crossed.  The 
condition  of  neighboring  culverts  and  bridge  openings  during 
floods  should  be  investigated,  and  the  nature  of  the  channel  of 
the  stream  and  the  character  of  its  drainage  basin  ascertained. 
Such  records  are  not  only  helpful  in  determining  the  size  of  the 
structure  under  consideration  but  are  of  value  in  showing  the 
degree  of  reliance  that  can  be  placed  on  a  waterway  formula. 

A  formula  widely  used  in  the  Central  States  was  proposed  in 
1887  by  Prof.  A.  N.  Talbot.  The  area  in  square  feet  of  the  net 
waterway  is  found  by  multiplying  the  three-fourths  power  of  the 
acres  drained  by  a  coefficient.  This  coefficient  was  taken  by 
Professor  Talbot  as  0.33  for  rolling  farming  land  subject  to  floods 
when  snow  melts  and  the  valley  drained  is  three  or  four  times  as 
long  as  it  is  wide,  0.16  to  0.2  in  districts  not  affected  by  snow  and 
with  the  valleys  several  times  longer  than  wide,  and  from  0.67  to 
1.0  for  steep,  rocky  ground.  The  waterways  given  by  this  for- 
mula are  stated  in  the  table  on  the  next  page. 


DRAINAGE,    CULVERTS   AND   BRIDGES 


31 


Square  Feet  of  Waterway  Required  by  Talbot's  Formula  for  Passing  the  Runoff 
from  Areas  Stated  of  Different  Classes  of  Land 


ACRES 
DRAIN- 
ED 

LEVEL 
LAND 

ROLL- 
ING 
LAND 

HILLY 
LAND 

MOUN- 
TAINOUS 

ACRES 
DRAINED 

LEVEL 
LAND 

ROLLING 

LAND 

HILLY 
LAND 

MOUN- 
TAINOUS 

10 

1.1 

2.3 

3.4 

4.5 

180 

9.8 

19.7 

29.5 

39.3 

20 

1.9 

3.8 

5.7 

7.6 

200 

10.6 

21.2 

31.8 

42.5 

30 

2.6 

5.1 

7.7 

10.2 

240 

12.2 

24.4 

36.6 

48.8 

40 

3.2 

6.4 

9.5 

12.7 

280 

13.7 

27.4 

46.1 

54.8 

50 

3.8 

7.5 

11.3 

15.0 

320 

15.1 

30.3 

45.4 

60.5 

60 

4.3 

8.6 

12.9 

17.2 

360 

16.5 

33.1 

49.6 

66.1 

70 

4.8 

9.7 

14.5 

19.4 

400 

17.9 

35.8 

53.7 

71.6 

80 

5.4 

10.7 

16.1 

21.4 

440 

19.2 

38.4 

57.6 

76.9 

90 

5.8 

11.7 

17.5 

23.4 

480 

20.6 

41.2 

61.8 

82.3 

100 

6.3 

12.6 

19.0 

25.3 

520 

21.8 

43.6 

65.3 

87.1 

120 

7.3 

14.5 

21.8 

29.0 

560 

23.0 

46.0 

69.1 

92.1 

140 

8.1 

16.3 

24.4 

32.6 

600 

24.2 

48.5 

72.7 

97.0 

160 

9.0 

18.0 

27.1 

36.1 

640 

25.4 

50.9 

76.3 

101.8 

About  1880  the  Santa  Fe  system  began  to  measure  accurately 
the  area  of  the  waterways  of  streams  during  floods  in  Missouri, 
Kansas,  Indian  Territory  and  Texas.  The  work  was  done  as 
carefully  as  possible  and  in  1897  the  results  were  summarized 
and  a  table  of  waterway  areas  issued  by  James  Dun,  chief  engi- 
neer of  the  system,  for  the  use  of  his  engineers.  The  collecting 
of  such  information  was  continued  after  that  date,  and  in  1906 
an  enlarged  table  was  printed  for  public  use,  which  is  extensively 
employed  by  railway  and  highway  engineers  in  the  section  of  the 

Square  Feet  of  Waterway  Given  by  Dun's  Table  for  Passing  the  Runoff  from 
Areas  Stated;  Applicable  to  Missouri  and  Kansas 


Area,  square  mile 

Waterway,  square  feet. 


Area,  square  mile 

Waterway,  square  feet. 


Area,  square  mile 

Waterway,  square  feet. 


Area,  square  mile 

Waterway,  square  feet. 


Area,  square  mile 

Waterway,  square  feet. 

Area,  square  mile 

Waterway,  square  feet. 


Area,  square  mile 

Waterway,  square  feet. 


0.01 
2.0 


0.100.150.200.250.300.350.400.45 


16 


0.550.600.650.700.750.800.850.90 


70 

1.0 

100 

1.9 
190 

3.6 
357 

6.0 
509 


0.020.030.040.050.060.070.080.09 


4.0 


25 


74 

1.1 
110 

2.0 
200 

3.8 
373 

6.5 
533 


6.0 


32 


78 

1.2 
120 

2.2 
220 

4.0 

388 

7.0 
556 


7.5 


38 


81 

1.3 
130 

2.4 

240 

4.2 
403 

7.5 

579 


9.0 


44 


85 

1.4 

140 

2.6 
260 

4.4 
417 

8.0 
601 


10.5 


51 


1.5 
150 

2.8 
280 

4.6 
430 

8.5 
622 


12.0 


56 


91 

1.6 
160 

3.0 
300 

4.8 
443 

9.0 
641 


62 


94 

1.7 
170 

3.2 
321 

5.0 

455 

9.5 
660 


15 

0.50 
66 

0.95 
97 

1.8 
180 

3.4 
340 

5.5 

483 

10.0 
679 


32 


AMERICAN  HIGHWAY   ASSOCIATION 


country  mentioned.  A  portion  of  the  table  is  reproduced  here. 
Mr.  Dun  stated  that  it  did  not  give  waterways  large  enough  for 
the  floods  that  occurred  at  very  long  intervals  and  were  of  un- 
precedented severity,  for  which  he  did  not  consider  it  advisable 
for  provision  to  be  made.  He  recommended  waterways  60  to 
80  per  cent  as  large  as  those  tabulated  for  culverts  and  bridge 
openings  in  Illinois,  about  5  per  cent  larger  waterways  for  Texas 
when  the  areas  drained  exceeded  1  square  mile,  and  from  1  \  to  6J 
per  cent  smaller  waterways  in  New  Mexico  for  areas  exceeding 
1  square  mile. 

About  thirty  years  ago,  C.  C.  Wentworth,  of  the  engineering 
staff  of  the  Norfolk  &  Western  Railway,  made  a  careful  study 
of  the  area  of  the  culverts  which  had  proved  of  sufficient  size  on 
that  road,  and  found  that  for  drainage  basins  of  one  acre  and 
upward,  the  square  feet  of  culvert  cross-section  should  be  equal 
to  the  two-thirds  power  of  the  number  of  acres  drained.  This 
formula  has  been  used  for  many  years  on  that  railway  and  found 
entirely  satisfactory.  The  accompanying  table  gives  the  areas 
computed  by  it  for  a  number  of  drainage  districts.  These  re- 
lations hold  good  quite  generally  over  the  area  between  the  Blue 
Ridge  and  the  Ohio  River,  and  have  been  found  to  agree  with 
flood  discharges  in  Maine,  Connecticut,  and  New  York.  It 
has  been  suggested  that  with  rainfalls  of  less  intensity  or  flatter 
slopes  than  those  of  the  section  which  furnishes  the  data  on  which 
the  formula  is  based,  the  areas  of  necessary  waterways  may  be 
taken  at  some  percentage  of  those  given  by  the  formula. 

Square  Feet  of  Waterway  Required  to  Discharge  the  Runoff  from  Areas  of  1 
to  99  Acres,  Computed  by  the  Wentworth  Formula  


0 

1.0 

2.0 

3.0 

4.0 

5.0 

6.0 

7.0 

8.0 

9.0 

0 

1.0 

1.6 

2.1 

2.5 

2.9 

3.3 

3  7 

4  0 

4.3 

10 

4.6 

4.9 

5.2 

5.5 

5.8 

6.1 

6.3 

6.6 

6.9 

7.1 

20 

7.4 

7.6 

7.9 

8.1 

8.3 

8.5 

8.8 

9.0 

9.2 

9.4 

30 

9.7 

9.9 

10.1 

10.3 

10.5 

10.7 

10.9 

11.1 

11.3 

11.5 

40 

11.7 

11.9 

12.1 

12.3 

12.5 

12.7 

12.8 

13.0 

13.2 

13.4 

50 

13.6 

13.8 

13.9 

14.1 

14.3 

14.5 

14.6 

14.8 

15.0 

15.1 

60 

15.3 

15.5 

15.7 

15.8 

16.0 

16.2 

16.3 

16.5 

16.7 

16.8 

70 

17.0 

17.2 

17.3 

17.4 

17.6 

17.8 

18.0 

18.1 

18.3 

18.4 

80 

18.6 

18,7 

18.9 

19.0 

19.2 

19.3 

19.4 

19.6 

19.8 

19.9 

90 

20.1 

20.2 

20.4 

20.5 

20.7 

20.8 

21.0 

21.1 

21.3 

21.4 

Culverts 

As  the  amount  of  water  to  be  carried  across  the  roadway  by  a 
culvert  is  usually  small,  the  majority  of  such  structures  are  made 
of  some  kind  of  pipe.  The  defects  which  such  culverts  develop 


DRAINAGE,    CULVERTS   AND    BRIDGES  33 

at  times  are  generally  due  to  lack  of  attention  to  features  essen- 
tial for  good  construction.  The  pipe  must  be  laid  on  a  perfect- 
ly firm  support.  If  the  trench  for  it  is  cut  too  low  and  must  be 
leveled  by  replacing  some  of  the  material,  the  latter  should  be 
consolidated  thoroughly  before  the  pipe  is  laid,  and  as  it  takes 
considerable  time  to  do  this  properly,  it  pays  to  be  careful  to 
excavate  in  the  first  place  to  the  exact  grade.1  After  the  pipe 
has  been  laid  and  the  joints  filled  if  it  is  made  of  bell-and-spigot 
lengths,  the  backfilling  should  be  done  with  the  same  care  used 
in  good  sewerage  work.  The  earth  should  be  rammed  thorough- 
ly around  the  sides  of  the  pipe,  taking  care  not  to  disturb  it  in 
doing  this,  and  not  more  than  6  inches  of  earth  should  be  spread 
without  ramming.  The  2  feet  of  fill  immediately  over  the 
pipe  should  be  similarly  placed  in  6-inch  layers  and  rammed, 
and  while  the  material  above  this  need  not  be  placed  so  carefully 
it  should  be  thoroughly  consolidated. 

The  inlet  and  outlet  of  the  pipe  should  be  at  the  bottom  of  the 
ditches  it  connects  or  at  the  level  of  the  bed  of  the  brook  that  it 
carries  across  the  road.  Each  end  should  have  a  wall  or  facing 
resting  on  an  absolutely  firm  foundation  far  enough  below  the 
surface  to  remain  unaffected  by  frost  and  heavy  enough  to  hold 
back  the  bank  resting  against  it.  Concrete  makes  the  best 
facing,  but  substantial  masonry  and  heavy  planks  have  given 
good  service  when  properly  used.  By  locating  and  protecting 
the  ends  of  the  pipe  in  this  way  two  important  advantages  are 
gained,  first,  the  thorough  drainage  of  the  side  ditches  and, 
second,  the  prevention  of  undercutting  of  the  ends  of  the  pipe. 
If  the  bottom  of  the  ditch  or  bed  of  the  brook  is  soft,  it  should  be 
payed  for  some  feet  above  and  below  the  culvert  to  prevent 
serious  erosion  during  severe  storms.  At  irregular  intervals 
several  years  apart  the  ditches  and  brooks  are  exceptionally 
flooded  and  the  water  is  liable  to  rise  above  the  top  of  the  pipe. 
If  the  culvert  has  been  constructed  as  just  recommended  no 
danger  need  be  feared,  for  the  road  will  act  as  a  dam  for  a  few 
hours  until  these  excessive  quantities  of  water  are  discharged. 
A  poorly  built  culvert  is  likely  to  be  washed  out,  however,  and 
carry  part  of  the  road  with  it.  Standard  plans  for  culvert  head- 
walls  can  be  obtained  from  most  State  highway  departments  and 
from  the  United  States  Office  of  Public  Roads  and  Rural  Engineer- 
ing at  Washington. 

Where  a  pipe  culvert  is  carried  across  a  side-hill  road,  dis- 
charging on  the  outer  slope,  some  form  of  channel  is  often  neces- 
sary for  carrying  the  water  down  the  side  of  the  embankment 

1If  the  sub-grade  is  soggy  it  is  well  to  lay  the  pipe  on  a  concrete  floor 
running  from  the  foundation  of  one  headwall  to  that  of  the  other.  Belt 
joints  should  be  laid  up-hill. 


34  AMERICAN   HIGHWAY  ASSOCIATION 

without  causing  erosion.  Gutters  of  rough  stone  paving,  con- 
crete channels  and  metal  troughs  have  all  been  used  for  this 
purpose. 

When  a  culvert  is  formed  of  two  pipes  laid  side  by  side,  which 
is  desirable  where  the  grades  are  very  flat,  or  the  bed  of  the  brook 
is  wide  and  the  depth  of  water  shallow  even  after  heavy  rains, 
particular  care  must  be  exercised  in  consolidating  the  filling  be- 
tween the  pipes. 

In  a  few  places,  where  timber  is  abundant  and  cheap,  cul- 
verts of  heavy  plank  are  used,  but  at  the  best,  they  are  only 
temporary  structures,  and  it  is  unwise  to  put  temporary  works 
which  are  costly  to  replace  in  a  roadway  graded  to  permanent 
lines.  The  same  is  true  of  box  culverts  of  dry  masonry,  with 
unpaved  bottoms.  Masonry  culverts  laid  carefully  in  cement 
mortar  are  rarely  so  cheap  as  permanent  pipe  or  concrete  cul- 
verts. Plans  and  instructions  for  building  concrete  culverts 
can  be  obtained  on  application  from  most  State  highway  de- 
partments and  from  the  United  States  Office  of  Public  Roads 
and  Rural  Engineering. 

Any  type  of  concrete  culvert  should  be  built  carefully  or 
frost  will  cause  trouble  with  it.  The  sand  and  gravel  or  broken 
stone  must  be  clean  and  graded  so  as  to  give  a  dense  mixture, 
and  the  mixing  of  the  mortar  must  be  thorough.  The  forms 
must  be  strong  and  tight  and  located  so  that  the  structure  will 
be  true  to  grade.  The  headwalls  in  particular  should  be  carried 
down  to  a  secure  foundation,  and  piling  or  a  substantial  timber 
platform  should  be  used  to  carry  the  concrete  in  case  there  is 
any  doubt  whatever  of  the  supporting  power  of  the  underlying 
material. 

The  general  tendency  of  rapidly  flowing  streams  is  to  lower 
their  beds.  This  results  in  time  in  leaving  the  culvert  floor 
rather  high  for  the  natural  bed  of  the  stream  and  the  water  finds 
its  way  underneath.  A  substantial  cross  wall  at  the  outlet  end  of 
the  culvert,  carried  well  below  possible  wash,  is  effective  in  stop- 
ping this  class  of  under-cutting,  A  frozen  earth  floor  will  some- 
times act  like  a  plank  floor  in  causing  such  undercutting,  and 
hence  good  cross-walls  are  advisable  in  all  culverts,  whether 
floored  or  not.  If  the  channels  leading  to  or  from  a  culvert  are 
in  soft  material  liable  to  erosion,  they  should  be  paved  or  pro- 
tected by  brush  and  heavy  stones. 

Bridges 

Structures  with  a  clear  span  exceeding  6  feet  are  generally 
classed  as  bridges  and  should  be  permanent  improvements  on  any 
road  brought  to  final  grade  and  alignment.  There  has  been 


DRAINAGE,    CULVERTS   AND    BRIDGES  35 

such  great  waste  of  money  in  past  years  on  the  bridges  on  rural 
roads  that  the  highway  departments  of  most  states  have  prepared 
standard  plans  and  specifications  which  cover  most  needs  of 
local  road  officials,  and  similar  standards  have  been  prepared 
by  the  United  States  Office  of  Public  Roads  and  Rural  Engi- 
neering. Structures  of  this  character  should  only  be  built  under 
competent  engineering  supervision,  both  as  to  substructures  and 
superstructures.  There  is  an  unfortunate  tendency  on  the  part 
of  highway  commissions  to  endeavor  to  save  money  by  omitting 
desirable  precautions  such  as  piling,  which  insure  the  safety  of 
the  bridges  under  conditions  which  an  engineer  recognizes  as 
dangerous.  For  example,  an  unusually  heavy  rainfall  in  north- 
eastern Iowa  in  June,  1916,  washed  out  163  bridges.  Some  were 
old  structures  that  needed  replacing  at  an  early  date,  but  others 
were  expensive  new  structures  of  good  design  and  construction 
except  for  the  fatal  omission  of  the  piling  under  the  founda- 
tions which  was  recommended  by  the  engineers  but  left  out  to 
reduce  the  cost.  Not  a  bridge  built  according  to  the  standards 
of  the  State  highway  commission  was  damaged. 

There  are  many  bridges  which  have  been  in  service  for  a  long 
period  of  time  without  suffering  any  injury,  although  their  sub- 
structures are  in  streams  with  an  easily  eroded  bottom  and  banks. 
For  example,  the  Walhouding  aqueduct  on  the  Ohio  canal  system, 
built  about  1830,  has  four  piers  and  two  abutments  in  a  stream 
with  a  fairly  swift  current,  rising  suddenly  to  a  great  height. 
Both  its  banks  and  bed  near  the  aqueduct  are  rapidly  eroded 
unless  protected.  The  piers  and  abutments  rest  on  double  plat- 
forms of  hewn  timbers,  laid  crosswise  and  carried  by  piles  driven 
close  together  near  all  four  sides  of  each  base.  Brush  and  heavy 
stone  were  placed  on  the  river  bed  around  each  foundation  and 
a  row  of  strong  piles  was  driven  across  the  river  bed  just  below 
the  aqueduct  to  prevent  the  removal  of  the  brush  and  stones  by 
the  current.  Such  a  record  of  endurance  made  by  structures 
built  before  the  beginning  of  the  present  era  of  scientific  engi- 
neering shows  how  needless  are  most  of  the  washouts  of  expen- 
sive bridges  that  occur  every  year. 

As  bridges  on  improved  roads  should  be  permanent  struc- 
tures, they  should  be  designed  to  carry  a  heavy  roller  followed 
'by  a  trailer  loaded  with  coal.  A  bridge  capable  of  supporting 
a  15-ton  roller  will  carry  any  of  the  heaviest  field  guns  now 
used  in  Europe. 

Money  is  saved  by  having  the  plans  and  specifications  for 
bridges  of  reinforced  concrete  or  steel  prepared  by  an  expe- 
rienced engineer,  so  that  all  bidders  on  its  construction  will  base 
their  estimates  on  the  same  structure  and  that  structure  will  be 
adapted  to  the  locality  and  service.  If  each  bidder  must  prepare 


36  AMERICAN   HIGHWAY   ASSOCIATION 

his  own  plans,  the  expense  of  doing  so  is  added  to  the  cost  of  the 
fabrication  of  the  steel  and  the  erection  of  the  structure.  This 
makes  a  general  increase  in  the  cost  of  bridges  in  a  district  where 
the  practice  is  followed,  for  many  unsatisfactory  plans  must 
be  prepared  for  one  that  is  satisfactory.  Furthermore  the  com- 
mission awarding  the  contract  must  not  only  pick  out  the  lowest 
bidder  but  also  decide  which  is  the  best  plan,  which  may  not 
be  that  offered  at  the  lowest  price. 

In  level  country  where  a  stream  overflows  its  banks  during 
heavy  floods  and  bridges  above  the  flood  level  require  long  expen- 
sive approaches,  what  are  known  as  overflow  bridges  are  coming 
into  quite  extensive  use.  They  are  structures  designed  to  be 
submerged  by  the  floods  and  to  offer  as  little  obstruction  as  pos- 
sible to  the  water  passing  over  them.  If  the  floods  are  likely 
to  carry  large  quantities  of  brush,  the  bridges  are  kept  partic- 
ularly low  so  the  brush  will  pass  freely  over  them  when  they  are 
submerged.  The  roads  leading  to  a  number  of  such  bridges 
have  concrete  pavements  extending  to  the  limits  of  the  sub- 
merged areas,  for  earth,  gravel  and  broken  stone  roads  are  liable 
to  serious  injury  from  water  flowing  across  them.  As  the  injury 
to  overflowed  embankments  generally  starts  at  the  top  of  the 
downstream  slope,  the  latter  is  often  protected  against  scouring 
by  covering  it  with  heavy  stone.  Stone  with  rounded  edges  is 
less  suitable  for  this  purpose  than  stone  of  an  angular  shape, 
because  the  former  is  rolled  about  more  easily. 

Fords 

Where  money  is  limited,  the  cost  of  building  even  a  submerged 
bridge  is  heavy,  and  the  stream  to  be  crossed  is  shallow,  a  ford 
is  sometimes  constructed  as  a  serviceable  temporary  expedient. 
In  Washington  County,  Utah,  for  example,  there  is  a  stream  with 
a  sandy  bottom  which  is  dry  at  some  seasons  and  dangerous 
during  floods  on  account  of  the  treacherous  nature  of  the  wet 
sand.  A  ford  has  been  constructed  which  consists  of  two  rubble 
walls  4  feet  deep  and  2  feet  wide,  with  a  2-foot  rubble  fill  between 
them.  The  entire  width  of  this  rubble  fill  from  one  wall  to  the 
other  is  20  feet,  and  the  stones  of  which  it  is  made  were  laid  in 
a  dense  mixture  of  sand  and  clay,  which  is  not  easily  washed  out 
of  the  voids  between  the  stones.  The  upstream  wall  was  laid 
dry  but  had  16  inches  of  clay  puddled  against  the  entire  depth 
of  its  outer  face.  The  downstream  wall  was  laid  in  lime  mortar. 

Near  Shelbyville,  Tennessee,  fords  have  been  made  passable 
at  all  times  by  constructing  a  number  of  parallel  culverts  close 
together  to  carry  the  usual  flow  of  the  stream  and  building  a 
concrete  roadway  over  these  culverts  to  give  a  safe  footing  for 
horses  and  a  secure  roadway  for  automobiles  during  high-water 
when  the  roadway  is  submerged. 


EARTH  AND  SAND-CLAY  ROADS1 

As  a  very  large  proportion  of  our  country  roads  must  be  earth 
roads  for  many  years  and  the  basis  for  any  type  of  surfaced  high- 
way is  a  properly  located,  drained  and  graded  earth  road,  the  rela- 
tive importance  of  this  type  is  very  great.  If  earth  roads  were 
properly  constructed  and  maintained,  and  their  culverts  and 
bridges  were  permanent  structures,  a  large  part  of  the  road  taxes 
now  wasted  would  produce  useful  returns.  It  is  proper  for  both 
highway  commissions  and  engineers  to  devote  a  large  part  of 
their  time  and  money  to  the  improvement  of  the  main  roads 
which  are  of  service  to  the  largest  number  of  taxpayers,  but  there 
is  a  deplorable  lack  of  efficiency  in  the  care  of  the  local  dirt  roads  in 
many  parts  of  the  country.  In  some  States,  of  which  New  York, 
Illinois  and  Iowa  are  examples,  these  roads  are  under  some  super- 
vision, directly  or  indirectly,  by  the  State  highway  department, 
but  generally  the  local  authorities  do  as  they  please.  For  in- 
stance, in  1916  there  were  71,000  miles  of  roads  in  Wisconsin  in 
sole  charge  of  local  officials,  who  spent  about  $4,500,000  on  them. 
The  work  was  subdivided  among  nearly  13,000  road  districts, 
each  with  a  road  supervisor,  and  there  were  3750  members  of  town 
boards  with  general  control  over  road  work.  Of  these  16,750 
officials,  about  one-fifth  drop  out  of  office  annually.  During 
the  ten  years  ending  December  31,  1916,  nearly  50,000  men 
were  in  charge  of  local  road  work  and  over  $40,000,000  spent  by 
them,  with  few  perceptible  lasting  improvements.  A  system 
giving  such  results  is  manifestly  wrong,  and  should  be  replaced 
by  one  with  a  smaller  number  of  road  officials  having  greater 
authority  and  responsibilities  and  serving  longer  terms.  It  will 
seem  from  the  following  notes  that  the  construction  and  mainte- 
nance of  earth  roads  calls  for  executive  ability  and  skill  that  can- 
not be  obtained  unless  fair  permanence  in  office  is  assured. 

The  construction  of  earth  roads  falls  into  two  general  classes, 
that  where  there  are  cuts  and  fills  and  that  where  the  road  is 
formed  by  building  a  low  embankment  on  the  surface.  Except 
where  the  length  of  road  is  great  enough  to  use  elevating  graders 
with  economy,  these  two  classes  are  generally  built  by  different 
methods. 

1  Revised  by  W.  S.  Keller,  State  Highway  Engineer  of  Alabama. 

37 


38  AMERICAN  HIGHWAY  ASSOCIATION 

Cuts  and  Fills 

In  grubbing  roots  and  breaking  hard  ground  to  a  shallow  depth, 
a  rooter  plow  is  often  used,  which  is  a  heavy  type  of  subsoil  plow 
made  for  the  purpose.  The  road  plow  is  a  heavy  form  of  turning 
plow  used  in  hard  ground  where  the  cuts  are  shallow.  Either 
type  is  drawn  by  four  to  eight  horses  or  a  tractor.  Plows  are 
also  specially  made  for  pushing  soil  already  loosened  from  ditches 
toward  the  center  of  the  road. 

When  the  cut  is  more  than  a  few  feet  in  depth  and  the  mate- 
rial loosened  with  difficulty,  it  is  often  blasted.  The  fastest  and 
most  economical  method  of  doing  this  is  to  sink  holes  across  the 
cut  on  a  line  back  from  the  face  a  distance  about  one-fourth 
greater  than  the  depth  of  the  cut  and  about  the  same  distance 
apart.  When  the  cut  is  6  feet  or  more  deep,  the  line  of  holes 
is  kept  about  6  feet  from  the  face  and  the  holes  are  sunk  about 
6  feet  apart.  They  are  loaded  with  a  low-strength  explosive 
and  care  must  be  taken  not  to  loosen  the  ground  below  the  fin- 
ished grade  line.  The  use  of  explosives  in  road  grading  in  other 
material  than  rock  has  been  extending  rapidly  on  account  of  its 
low  cost  and  the  rapid  progress  that  can  be  made  under  suitable 
conditions,  for  the  blasts  leave  the  clay  or  hardpan  in  a  broken 
up  condition  making  it  easy  to  handle.  On  side-hill  cuts  in  heavy 
ground,  where  the  slope  is  steep  and  there  is  some  question  about 
the  security  of  an  embankment  to  carry  the  outer  part  of  the 
road,  a  safe  roadway  can  often  be  blasted  out  of  the  hill  at  a  cost 
comparing  favorably  with  a  road  partly  supported  by  a  retain- 
ing wall.  Even  on  easier  slopes,  where  a  long  side-hill  cut  in 
heavy  ground  must  be  made  and  the  excavated  material  can  be 
employed  as  an  embankment  to  carry  the  outer  part  of  the  road- 
way, the  excavation  is  often  made  by  blasting.  Blasting  is 
also  an  effective  method  of  breaking  up  stumps  and  boulders. 

Where  the  material  is  easily  handled  and  can  be  dumped  within 
100  feet  of  the  cut,  slip  scrapers  are  generally  regarded  as  the 
least  expensive  equipment.  The  Fresno  scraper  is  regarded  as 
better  than  the  slip  scraper  for  hauls  exceeding  100  feet.  If  the 
haul  exceeds  100  feet  and  is  under  1000  feet,  wheel  scrapers  are 
ranked  highly.  The  large  sizes  are  most  desirable  for  econ- 
omy on  hauls  over  600  feet.  The  material  is  usually  plowed  so 
the  wheelers  can  be  loaded  easily,  and  it  is  necessary  to  have 
about  one  of  them  for  every  100  feet  of  haul  in  order  to  work 
most  economically.  Bottom-dump  wagons  can  be  made  to  give 
very  low  hauling  costs  if  enough  are  provided  so  that  while  one  is 
being  loaded  at  the  cut,  the  driver  and  team  which  brought  it  in 
can  be  used  in  hauling  a  loaded  wagon. 

In  recent  years  traction  steam  shovels  have  been  growing  stead- 


EAKTH  AND  SAND-CLAY  EOADS  39 

ily  in  favor  for  road  grading.  They  make  shallow  cuts  as  easily 
as  deep  cuts,  and  have  taken  out  earth  and  rock  at  very  low 
figures  when  the  equipment  for  removing  the  excavated  mate- 
rial was  properly  selected  and  used  so  as  to  keep  the  shovel  work- 
ing most  of  the  time.  The  economy  of  steam  shovel  operation 
depends  upon  the  proportion  of  the  working  day  that  it  is  ac- 
tually digging,  and  this  depends  upon  having  wagons  or  cars 
ready  to  receive  the  excavated  material.  The  wagons  or  cars 
may  often  be  run  along  the  top  of  the  bank  of  a  shallow  cut 
and  kept  moving  in  a  continuous  line,  saying  the  delay  of  turn- 
ing  and  backing  up  to  the  shovel,  which  is  necessary  when 
they  move  over  the  graded  cut.  The  utility  of  a  shovel  on  road- 
work  is  increased  if  it  can  be  employed  in  a  gravel  pit  or  quarry 
when  not  grading. 

The  bottom  of  the  cut  should  be  carried  down  approximate- 
ly parallel  to  the  finished  cross-section,  and  care  should  be  taken 
not  to  disturb  the  material  below  the  grade  line.  In  very  heavy 
ground,  the  final  trimming  is  sometimes  done  by  hand,  but  gen- 
erally a  road  machine  can  be  used  to  advantage. 

Where  a  fill  is  made,  the  surface  must  be  cleared.  Stumps 
should  be  grubbed  out1  and  all  large  material  liable  to  decay 
should  be  removed,  for  if  left  in  place  the  fill  will  settle  as  it  rots 
or  have  loose  places  likely  to  retain  moisture.  If  the  fill  is  on 
a  steep  side-hill,  the  latter  should  be  cut  into  a  series  of  level 
benches  or  steps  and  the  drainage  should  receive  careful  atten- 
tion. If  the  hill  has  a  gentle  slope,  it  is  usually  sufficient  to  plow 
parallel  furrows,  which  will  furnish  a  sufficiently  uneven  surface 
to  hold  the  fill.  The  object  in  any  case  is  to  unite  the  material 
in  the  bottom  of  the  embankment  with  that  of  the  hillside. 

If  the  road  will  be  maintained  as  an  earth  road  for  several 
years,  so  it  will  have  ample  time  to  become  consolidated  under 
traffic  before  any  surfacing  is  applied,  there  is  usually  little  rea- 
son for  limiting  the  thickness  of  the  layers  in  which  the  embank- 
ment is  built.  But  if  a  surfacing  is  to  be  given  the  road  at  an 
early  date,  the  layers  should  not  exceed  2  feet  for  high  fills  and 
1  foot  for  low  fills.  The  teams  and  scrapers  moving  over  the 
fill  compact  it  to  some  extent.  Formerly  little  attention  was 
paid  to  smoothing  the  surface  of  the  layers,  but  of  late  this  has 
been  considered  important  in  some  states  and  drags  are  kept 
at  work  on  a  bank  a  large  part  of  the  time.  George  W.  Cooley, 
State  engineer  of  Minnesota,  has  explained  this  leveling  work 
as  follows: 

1  It  is  not  customary  in  the  South  to  require  green  stumps  and  roots  to 
be  grubbed  where  the  fill  over  their  tops  is  as  much  as  18  inches.  Any 
matter  in  process  of  decay  must  be  removed  but  a  green  stump  sealed  in  a 
fill  so  that  air  will  not  reach  it  lasts  forever. 


40  AMEEICAN   HIGHWAY   ASSOCIATION 

In  Minnesota  the  plan  has  been  adopted  in  the  construction  of  earth 
roads  to  require  the  continual  use  of  a  drag  or  planer  on  grade  building. 
This  latter  plan  has  been  found  very  efficient  and  renders  future  work  on 
the  surface  less  expensive,  besides  tending  to  produce  a  more  compact 
road  bed.  The  tool  found  most  satisfactory  in  this  work  is  that  known 
as  the  "Minnesota  road  plane,"  which  consists  of  the  two  blades  of  an  ordi- 
nary road  drag,  fixed  between  a  pair  of  runners  about  14  feet  long,  the  blades 
set  at  an  angle  of  about  60  degrees  to  the  runner  and  made  rigid  or  adjust- 
able as  may  be  deemed  best.  The  planer  is  hauled  on  a  line  parallel  with 
the  axis  of  the  road  and  its  operation  is  similar  to  that  of  the  ordinary  drag, 
with  the  additional  advantage  of  making  a  smoother  surface.  The  old 
style  drag  without  runners  has  a  tendency,  especially  on  new  work,  to 
increase  the  waves  or  undulations  frequently  occurring  on  road  construc- 
tion, while  the  planer  eliminates  these  faults  and  as  a  general  maintenance 
tool  has  proved  the  most  satisfactory. 

All  embankments  settle  or  "shrink"  for  some  time  after  they 
have  been  built.  If  the  material  is  broken  into  small  pieces  and 
trampled  by  teams,  the  shrinkage  will  be  less  than  if  it  is  dumped 
in  large  masses.  There  is  little  shrinkage  in  a  well-built  earth 
dam  to  impound  water,  but  road  embankments  need  not  be 
built  so  carefully,  and  it  is  probably  desirable  to  allow  for  at 
least  10  per  cent  shrinkage  of  embankments  over  3  feet  high  and 
at  least  15  per  cent  for  those  under  3  feet.  If  loamy  material  is 
used  in  the  embankments  the  shrinkage  will  probably  be  greater 
than  this. 

Grader  Work 

A  large  part  of  the  earth  roads  now  built  or  reconstructed  are 
made  with  road  machines.  These  are  built  in  many  sizes  for 
both  horse  and  tractor  hauling,  and  serve  a  variety  of  purposes 
in  an  economical  manner.  They  are  not  adapted  for  making 
cuts  and  fills,  although  frequently  employed  in  shaping  a  road 
after  the  grading  has  been  done.  The  method  of  using  the 
machine  on  construction  is  explained  in  the  following  instruc- 
tions prepared  by  W.  S.  Gearhart,  State  engineer  of  Kansas: 

In  building  new  roads  with  a  road  grader  the  dead  weeds  and  grass 
should  first  be  burned  off  before  any  grading  work  is  done,  and  the  width 
of  the  road  to  be  graded  should  be  staked  so  the  ditches  can  be  properly 
lined  up.  Then  plow  a  light  furrow  with  the  point  of  the  grader  blade, 
carrying  the  rear  end  of  the  blade  well  elevated.1  On  the  second  round 
drive  the  wheels  in  line  with  the  point  along  the  hollow  made  the  first 
round,  plowing  a  full  furrow  with  tne  advance  end  of  the  blade,  dropping 
the  rear  end  somewhat  lower  than  before.  The  third  time  mova  toward 
the  middle  of  the  road  the  earth  previously  plowed,  then  return  to  the 
ditch  and  plow  it  out  deeper,  moving  the  earth  toward  the  middle  when- 
ever as  much  has  been  plowed  as  the  machine  will  move  at  once.  Repeat 
this  process  until  the  ditches  are  the  proper  depth,  and  then  cut  off  the 
outer  slopes  of  the  ditches  by  placing  one  wheel  of  the  grader  in  the  bot- 
tom of  the  ditch  and  the  other  one  on  the  bank.  This  can  be  done  easily 

1 A  plow  is  necessary  in  breaking  up  the  ground  except  in  light  soils. 


EARTH  AND  SAND-CLAY  ROADS  41 

if  the  bank  is  not  more  than  30  inches  above  the  bottom  of  the  ditch.  Then 
trim  the  earth  to  the  true  cross-section.  Thoroughly  harrow  the  loose 
material  with  an  ordinary  straight-tooth  harrow  if  there  are  no  clods,  going 
over  it  until  the  bumps  have  been  leveled  off,  the  low  places  filled  up  and 
the  material  well  compacted.  If  there  are  sods  or  tough  lumps  of  earth 
in  the  road  a  disk  harrow  should  be  used  to  pulverize  this  material,  and 
the  disk  harrow  should  be  followed  by  a  drag  or  a  straight-tooth  harrow 
to  level  and  smooth  the  road.  No  newly  graded  road  can  be  finished  in 
good  shape  without  using  either  the  harrow  or  the  drag,  or  both. 

In  the  later  rounds  of  a  road  machine,  in  the  final  shaping 
of  the  road,  part  of  the  loose  material  in  the  center  of  the  road 
is  pushed  back  to  the  shoulders.  The  settlement  on  fills  will 
result  in  losing  about  2  feet  in  the  width  of  the  roadway,  and  the 
fills  should  be  made  wider  than  the  standard  sections  to  allow 
for  this  loss.  In  doing  this  final  work,  the  blade  of  the  grader 
is  set  at  an  angle  of  about  45  degrees  with  the  direction  of  travel, 
its  ends  adjusted  to  the  slope  of  the  road,  and  lowered  as  a  whole 
on  successive  rounds. 

If  the  work  is  on  a  scale  large  enough  to  warrant  the  use  of  two 
graders  hauled  by  a  tractor  or  roller,  a  trained  grading  crew  is 
often  able  to  build  a  good  roadbed  at  very  low  cost.  Mechani- 
cal traction  has  resulted  in  the  development  of  methods  of  con- 
struction impracticable  when  teams  of  four  to  eight  horses  were 
employed,  and  as  a  general  proposition  mechanical  traction  is 
most  economical  when  the  sections  to  be  graded  are  a  quarter 
of  a  mile  or  more  long,  and  there  is  enough  work  in  the  vicinity 
to  keep  a  tractor  busy  most  of  the  time.1  Time  lost  in  standing 
idle  or  moving  long  distances  from  one  grading  job  to  another 
reduces  the  economical  advantage  of  a  tractor  on  work  not  well 
organized.  In  many  cases  the  hauling  is  done  by  a  road  roller. 
Tractors  and  rollers  are  particularly  good  investments  where 
labor  and  teams  are  hired  at  high  rates  and  not  always  obtainable. 
Mechanical  traction  is  so  much  more  powerful  and  rapid  than 
horse  traction,  that  its  total  saving  on  road  work  can  only  be 
figured  by  including  the  saving  in  labor  charges  due  to  speedy 
construction. 

Where  road  grading  is  carried  on  by  day  labor  by  district  offi- 
cials, preparation  is  sometimes  made  for  it  in  late  fall  or  early 
spring  by  plowing  up  the  ground  along  the  lines  of  the  ditches 
and  slopes.  This  disintegrates  the  sod  and  prevents  the  roots 
of  grass  and  weeds  from  forming  clods  which  must  be  broken 
up  by  disk  harrows  or  thrown  out  of  the  road  with  forks.  While 
it  is  allowable  to  build  an  embankment  on  good  sod  after  it  has 
been  burned  over,  neither  sod  nor  any  other  organic  material 

1  Traction  grading  with  heavy  road  machines  is  better  adapted  for  some 
conditions  than  others,  and  the  advice  of  an  experienced  engineer  should  be 
obtained  before  purchasing  expensive  equipment 


42  AMERICAN   HIGHWAY  ASSOCIATION 

should  be  allowed  in  the  embankment  unless  reduced  to  small, 
disconnected  bits.  If  clods  are  left  in  a  fill,  particularly  in  the 
top,  it  is  very  difficult  to  maintain  by  dragging  a  hard,  uniform 
surface  free  from  depressions  and  waves. 

Grading  by  machines  is  often  followed  up  immediately  by 
hand  trimming  and  the  removal  of  loose  stone.  Easing  upon 
work  by  leaving  steep,  untrimmed  slopes  and  uneven  ditches 
results  in  heavier  maintenance  expense. 

In  organizing  grader  work,  it  is  desirable  to  keep  on  hand  re- 
pair parts  of  the  machines,  such  as  blades  and  whiffletrees,  as 
well  as  plow  points  and  other  parts  of  the  equipment  likely  to 
wear  out.  The  small  tools  should  be  selected  with  care,  for 
observation  by  efficiency  specialists  has  shown  that  the  shape 
of  a  shovel,  for  example,  has  considerable  effect  on  the  amount 
of  shoveling  a  man  can  accomplish  in  a  day.  Hard  earth  cannot 
be  dug  economically  by  the  shovel  best  adapted  for  loose  earth, 
and  neither  is  best  for  gravel  and  broken  stone. 

On  extensive  work  the  elevating  grader  has  proved  an  eco- 
nomical and  rapid  machine  when  a  mile  or  more  of  road  can  be 
traversed  without  turning  the  outfit.  Such  a  grader  is  often 
hauled  by  a  traction  engine,  which  rolls  the  material  it  passes 
over  and  thus  assists  materially  in  making  a  compact  road.  The 
method  of  using  the  grader  depends  upon  the  nature  of  the  work 
to  be  done.  In  cuts,  the  grader  often  discharges  the  excavated 
material  into  wagons  driven  beside  it  until  full.  These  wagons 
haul  the  material  to  the  nearest  fills.  In  light  cuts,  the  material 
is  deposited  on  the  roadway  and  moved  to  the  nearest  low  places 
in  the  road  by  slip  or  wheel  scrapers.  The  cut  is  usually  started 
at  the  shoulder  and  the  grader  moves  toward  the  roadside  on 
successive  rounds,  so  that  the  excavated  material  is  deposited 
nearer  and  nearer  to  the  center  of  the  road  by  the  elevating  and 
discharging  device.  The  road  should  be  dragged  during  con- 
struction, and  as  soon  as  the  rough  grading  is  finished  it  should 
be  shaped  at  once.  In  this  connection  attention  is  called  to 
the  following  comment  by  the  Iowa  highway  commission: 

The  impassable  condition  to  which  some  contractors  and  county  road 
crews  reduce  their  roads  while  cuts,  fills  and  other  improvements  are  being 
carried  out,  is  absolutely  inexcusable.  The  worst  conditions  usually 
arise  at  leveling  or  smoothing  up  while  dumping  is  in  progress.  The  dirt 
of  the  fill  so  dumped  packs  in  humps  so  that  sometimes  it  is  impracticable 
to  eradicate  the  unevenness  for  years.  A  little  care  in  spreading  the  dirt 
evenly  at  the  time  of  dumping  results  in  the  fill  packing  in  thin,  even  lay- 
ers instead  of  humps.  Such  a  road  is  travelable  during  construction, 
and  when  the  fill  is  completed  the  job  is  done.  A  Marshall  County  road 
crew  solved  the  problem  by  keeping  a  light  road  drag  at  hand.  From  time 
to  time  a  team  was  unhooked  from  a  scraper  and  hitched  to  this.  A  few 
minutes  work  put  the  freshly  dumped  material  into  thin  layers  instead 
of  humps. 


EAKTH  AND  SAND-CLAY  ROADS  43 

The  utility  of  a  road  roller  on  earth  roads  is  generally  under- 
estimated. After  the  earth  has  been  given  as  much  crown  as 
the  road  can  have  and  still  enable  the  traffic  to  use  its  entire  sur- 
face readily,  any  further  improvement  of  the  surface  drainage 
must  be  attained  by  decreasing  the  porosity  of  the  earth.  This 
can  be  done  by  oiling  the  road  as  described  later  in  the  section 
on  Surface  Applications,  and  by  reducing  the  pores  of  the  earth 
by  rolling.  The  latter  is  particularly  useful  in  compacting  places 
of  a  yielding  character.  Many  counties  have  purchased  rollers, 
placed  them  in  charge  of  competent  men,  and  rent  the  outfits 
to  the  townships  as  the  latter  need  them.  In  some  cases,  a  roller 
is  bought  by  a  number  of  townships,  acting  as  a  whole.  The 
work  of  a  roller  outfit  is  likely  to  be  unnecessarily  expensive  if 
it  is  not  carefully  planned  so  as  to  avoid  long  journeys  to  do  small 
jobs. 

Dragging 

Earth  roads  under  light  traffic  can  be  kept  in  good  condition 
during  a  large  part  of  the  year  by  dragging  and  proper  care  of 
the  ditches.  It  is  an  axiom  in  road  maintenance  that  defects 
in  the  surface  of  a  road  should  be  remedied  as  soon  as  they 
appear,  because  traffic  will  develop  them  quickly.  The  earth 
road  is  particularly  subject  to  injury  because  it  does  not  have 
hard  stone  locked  in  place  to  resist  the  destructive  effect  of  horses' 
shoes,  narrow  tires  and  pneumatic  tires.  On  the  other  hand  it 
is  more  easily  repaired  than  any  other  road,  because  as  soon  as 
its  surface  is  wet  by  rain  the  ruts  and  holes  can  be  filled  by  haul- 
ing a  drag  over  the  surface.  This  scrapes  material  from  the 
high  points  into  the  depressions  and  rubs  down  the  whole  sur- 
face. The  following  explanation  of  the  nature  of  the  improve- 
ment has  been  given  by  A.  R.  Hirst,  State  highway  engineer 
of  Wisconsin: 

If  a  sample  of  moist  earth  is  taken  from  the  traveled  portion  of  a  road 
over  a  gumbo,  clay  or  black  prairie  soil,  it  will  be  found  practically  imper- 
vious to  water,  as  may  be  proved  by  forming  a  roughly  shaped  dish  of  damp 
earth  and  filling  it  with  water.  It  will  be  noticed  that  the  dish  is  practi- 
cally water-tight.  Earth  in  this  condition  is  what  the  clay  workers  call 
puddled.  It  has  been  worked  and  reworked  by  the  carriage  wheels  and 
animals'  hoofs  until  nearly  all  the  traveled  portion  of  a  sticky  muddy 
road  is  covered  with  a  layer  of  this  impervious,  puddled  earth.  As  usually 
found  on  most  of  the  roads,  this  puddled  earth  is  full  of  holes  and  ruts, 
which  are  filled  with  water  that  cannot  escape  through  the  impervious 
soil.  As  long  as  the  water  remains  the  soil  cannot  dry  out  and  the  road 
is  kept  in  a  most  uncomfortable  if  not  impassable  condition.  It  is  also 
a  matter  of  observation  that  this  puddled  earth  when  compressed  and  dried 
becomes  extremely  hard.  On  these  two  facts,  the  imperviousness  of  pud- 
dled earth  and  its  hardness  when  dried,  rests  the  theory  of  road  dragging. 


44  AMERICAN   HIGHWAY  ASSOCIATION 

f  When  the  road  drag  is  properly  used  it  spreads  out  the  layer  of  imper- 
vious soil  over  the  surface  of  the  road,  filling  up  the  ruts  and  hollows  until 
a  smooth  surface  is  secured.  As  a  small  amount  of  material  is  always  to  be 
pushed  to  the  center,  a  slightly  rounded  effect  will  be  given  to  the  road, 
which  may  be  increased  or  decreased  as  desired  by  subsequent  dragging. 
By  forcing  the  mud  into  the  hollows  and  ruts  it  is  evident  that  the  water 
must  go  out,  which  it  does  by  running  off  to  the  side  of  the  road.  The 
drying  out  of  the  road  is  thus  much  facilitated  and  the  road  is  made  imme- 
diately firmer  because  the  water  is  squeezed  out.  The  effect  of  traffic 
over  the  road  tends  to  press  down  and  thoroughly  compact  each  thin 
layer  of  puddled  earth  which  the  drag  spreads  over  the  surface  every  time 
it  is  used.  After  the  first  few  draggings  it  will  be  noticed  that  the  road  is 
becoming  constantly  smoother  and  harder  so  that  the  effect  of  a  rain  is 
scarcely  noticeable,  the  water  running  off  the  surface  which  is  so  smooth 
and  hard  as  to  absorb  but  little  of  it. 

The  drag  is  an  old  implement.  It  was  described  in  a  book  by 
William  Gillespie  published  in  1851  and  widely  used  by  stu- 
dents of  engineering  and  public  officials,  yet  the  drag  did  not 
come  into  favor  until  about  1900.  Even  today  it  is  not  used  on 
more  than  a  small  percentage  of  the  roads  where  it  should  be 
employed  regularly.  It  has  a  number  of  forms,  the  essential 
feature  being  two  parallel  blades  held  vertically  or  nearly  so 
about  2J  feet  apart  by  a  frame  of  some  sort.  The  bottom  of 
each  blade  scrapes  over  the  surface  of  the  road.  The  rear  blade 
projects  12  to  16  inches  to  one  side  of  the  front  blade  so  that 
when  the  drag  is  pulled  at  an  angle  of  30  degrees,  the  ends  of  the 
blades  will  be  on  a  line  parallel  with  the  center  of  the  road.  The 
drag  is  hauled  by  a  chain,  to  which  the  team  can  be  hitched  at 
points  that  will  make  the  drag  lie  diagonally  on  the  road  as  it  is 
pulled  along.  The  manner  of  its  use  has  been  described  sub- 
stantially as  follows  by  the  United  States  Office  of  Public  Roads. 

Under  ordinary  circumstances  the  position  of  the  hitching  link  on  the 
draw  chain  should  be  such  that  the  runners  will  make  an  angle  of  from 
60  degrees  to  75  degrees  with  the  center  line  of  the  road,  or  in  other  words, 
a  skew  angle  of  from  15  degrees  to  30  degrees.  It  is  apparent  that  by 
shifting  the  position  of  the  hitching  link  the  angle  of  skew  may  be  in- 
creased or  diminished  as  the  conditions  require.  When  dragging  imme- 
diately over  ruts  or  down  the  center  of  the  road  after  the  sides  have  been 
dragged,  it  is  usually  preferable  to  have  the  hitching  link  at  the  center  of 
the  chain  and  to  run  the  drag  without  skew.  When  the  principal  pur- 
pose of  the  dragging  is  to  increase  the  crown  of  the  road,  the  drag  should 
be  sufficiently  skewed  to  discharge  all  material  as  rapidly  as  it  is  collected 
on  the  runners.  On  the  other  hand,  if  depressions  occur  in  the  road  sur- 
face, the  skew  may  perhaps  be  advantageously  reduced  to  a  minimum,  thus 
enabling  the  operator  to  deposit  the  material  which  collects  in  front  of  the 
runners  at  such  points  as  he  desires  by  lifting  or  otherwise  manipulating 
the  drag.  It  is  impracticable  to  prescribe  even  an  approximate  rule  for 
fixing  the  length  of  hitch,  because  it  is  materially  affected  by  the  height 
of  the  team  and  the  arrangement  of  the  harness,  as  well  as  by  the  condi- 
tion of  the  road  surface.  Experience  will  soon  teach  the  operator,  however, 
when  to  shorten  the  hitch  in  order  to  lessen  the  amount  of  cutting  done 


EAETH  AND  SAND-CLAY  ROADS  45 

by  the  front  runner  and  when  to  lengthen  it  in  order  to  produce  the  oppo- 
site effect.  Care  should  be  taken  that  a  ridge,  often  called  a  ''potato 
ridge,"  is  not  left  in  the  center  of  the  road. 

When  the  road  surface  is  sufficiently  hard  or  the  amount  of  material 
which  it  is  desired  to  have  the  drag  move  is  sufficient  to  warrant  the  oper- 
ator standing  upon  the  drag  while  it  is  in  operation,  he  can  greatly  facili- 
tate its  work  by  shifting  his  weight  at  proper  times.  For  example,  if  it  is 
desired  to  have  the  drag  discharge  more  rapidly,  the  operator  should  move 
toward  the  discharge  end  of  the  runners.  This  will  cause  the  ditch  end 
of  the  runners  to  swing  forward  and  thus  increase  the  skew  angle  of  the 
drag.  The  operator  may,  of  course,  produce  the  opposite  effect  by  moving 
his  weight  in  the  opposite  direction.  In  the  same  way,  he  can  partially 
control  the  amount  of  cutting  which  the  drag  does  by  shifting  his  weight 
backward  or  forward,  as  the  case  may  be. 

The  rule  frequently  cited,  that  all  earth  roads  should  be  dragged 
immediately  after  every  rain,  is  in  many  cases  entirely  imprac- 
ticable and  is  also  very  misleading  because  of  the  conditions 
which  it  fails  to  contemplate.  It  is  true  that  there  are  many 
road  surfaces  composed  of  earth  or  earthy  material  which  do 
not  become  very  muddy  under  traffic,  even  during  long  rainy 
seasons,  and  since  such  surfaces  usually  tend  to  harden  very 
rapidly  as  soon  as  the  weather  clears  up,  it  may  be  desirable  to 
drag  roads  of  this  kind  immediately  after  a  rain.  Such  roads, 
however,  would  not  ordinarily  need  to  be  dragged  after  every 
rain,  because  of  the  strong  tendency  that  they  naturally  possess 
of  holding  their  shape.  On  the  other  hand,  many  varieties  of 
clay  and  soil  tend  to  become  very  muddy  under  only  light  traffic 
after  very  moderate  rains,  and  it  is  evident  that  roads  constructed 
of  such  materials  could  not  always  be  successfully  dragged  imme- 
diately after  a  rain.  Sometimes,  in  fact,  it  may  be  necessary 
to  wait  until  several  consecutive  clear  days  have  elapsed  after 
a  long  rainy  spell  before  the  road  is  sufficiently  dried  out  to  keep 
ruts  from  forming  almost  as  rapidly  as  they  can  be  filled  by  drag- 
ging. In  many  cases  of  this  kind,  however,  it  is  possible  greatly 
to  improve  the  power  of  the  road  to  resist  the  destructive  action 
of  traffic  during  rainy  seasons  by  repeatedly  dragging  it  at  the 
proper  time. 

Maintenance  by  dragging  is  most  successful  when  well  organ- 
ized. The  results  obtained  by  good  management  in  Hopkins 
County,  Kentucky,  are  frequently  cited  as  indications  of  this, 
and  for  this  reason  the  following  account  of  the  work  there  is 
quoted  from  a  report  by  the  Kentucky  department  of  highways. 

In  1912  a  county  engineer  was  appointed.  The  county  roads  were 
measured  under  his  supervision  and  2-mile  sections  designated,  and  in 
January,  1913,  drags  were  started  on  about  100  miles  of  the  county  roads. 
This  original  contract  was  only  for  dragging  the  roads,  which  work  was 
to  be  done  four  times  between  January  1  and  April  1,  at  a  cost  of  $10  to 
$12  per  mile.  As  the  sections  dragged  were  not  continuous,  the  citizens 


46  AMERICAN   HIGHWAY  ASSOCIATION 

at  once  appreciated  the  difference  between  the  maintained  road  and  that 
which  was  not  maintained.  Consequently  the  next  contract,  which 
called  for  dragging  and  also  for  cleaning  the  ditches  for  six  months,  until 
November,  1913,  resulted  in  contracts  for  150  miles  of  road  and  at  a  re- 
duced cost.  In  November,  1913,  a  contract  substantially  like  that  now 
in  use  was  adopted  and  the  time  of  the  contract  was  for  one  year,  or  until 
November,  1914.  Over  200  miles  were  maintained  this  year  at  an  average 
cost  of  $28  per  year  per  mile.  For  the  year  from  November,  1914,  to  No- 
vember, 1915,  the  benefit  of  the  maintained  roads  was  so  well  understood 
by  the  citizens  that  560  miles  were  under  contract  at  an  average  cost  of 
$24.35  per  mile  per  year. 

In  November,  1915,  a  two-year  contract  was  entered  into,  which  the 
county  may  revoke  for  non-performance  of  the  obligation  at  the  end  of 
the  first  year.  About  520  miles  are  now  under  contract,  at  prices  ranging 
from  $12  to  $40  per  mile  per  year,  the  average  being  $22. 10.  It  is  expected 
this  mileage  will  soon  be  increased.  Originally  a  contractor  was  allowed 
to  have  charge  of  8  miles,  but  now  he  is  not  allowed  to  contract  for  more 
than  4  miles  of  road.  Under  the  1915  contracts  the  contractor  must  trim 
the  branches  which  overhang  and  interfere  with  travel  on  the  roadway; 
keep  the  roadway  between  ditches  free  from  shrubbery  and  weeds;  keep 
the  ditches  clean,  free  from  obstructions,  and  at  all  times  capable  of  car- 
rying the  water.  '  'He  shall  by  June  1  each  year  grade  the  roads  with  dump 
scraper,  grader,  drag  and  ditcher,  or  in  any  way  he  may  see  fit,  so  that  the 
center  of  the  roadway  shall  be  crowned  so  that  the  water  will  flow  from  the 
center  of  the  road  to  the  side  ditches,  and  at  no  place  will  the  water  stand 
on  the  road  or  run  down  the  road.  The  road  shall  be  dragged  from  ditch 
to  ditch  at  each  dragging,  when  the  road  is  wet,  but  not  sticky." 

A  record  of  the  number  of  draggings  is  kept  by  the  county  engineer 
on  cards  which,  before  mailing  by  the  contractor,  are  countersigned  by  the 
rural  route  carrier  or  a  reliable  citizen.  The  contractor  also  hauls  ma- 
terial and  constructs  all  culverts  and  bridges  of  10-foot  span  or  under,  and 
keeps  the  approaches  to  and  the  floors  and  abutments  of  all  bridges  and 
culverts  on  his  road  in  good  traveling  condition.  An  analysis  of  these 
contracts  shows  that  where  the  contract  has  been  faithfully  executed 
there  is  a  decrease  each  year  in  the  cost  per  mile,  mainly  because  the  far- 
mer contractor  has  learned  from  experience  that  continuous  maintenance 
makes  a  lower  cost  of  time  and  labor  each  succeeding  year. 

In  the  semi-arid  regions,  the  soil  is  often  of  a  very  light  nature, 
so  lacking  in  adhesive  qualities  that  strong  winds  or  flowing 
water  erode  it  and  travel  abrades  it  rapidly  into  fine  dust.  It  is  in 
its  best  condition  to  carry  travel  when  it  is  moist,  but  if  it  be- 
comes saturated  with  water  it  is  almost  impassable.  Chuck 
holes  a  foot  deep  are  formed  in  dry  weather  in  an  earth  road 
through  such  soil,  and  as  they  become  filled  with  light  dust  they 
are  a  serious  impediment  to  easy  travel.  Clay  or  gravel  con- 
taining clay  improves  the  roads  when  worked  into  them.  The 
ditches  should  be  wide  and  shallow,  rather  than  deep,  and  the 
crown  should  be  rather  low  for  an  earth  road,  in  order  to  retain 
moisture  in  the  roadbed.  For  the  same  reason,  all  grading  and 
ditching  are  best  done  just  before  or  during  the  rainy  season, 
in  order  to  have  plenty  of  water  to  pack  the  soil.  On  account 
of  the  pulverulent  nature  of  the  material,  the  ends  of  all  culverts 


EARTH  AND  SAND-CLAY  ROADS  47 

must  be  planned  carefully  and  riprap  or  some  other  material 
placed  to  prevent  erosion  about  the  inlets  and  outlets.  The  main 
problem  with  earth  roads  in  such  soils  is  to  keep  the  roadbed 
damp  and  to  incorporate  with  it  adhesive  or  fibrous  material 
which  will  act  as  a  binder. 

Sand-Clay  Roads 

The  grains  of  which  sand  is  composed  are  usually  hard  and 
tough  and  able  to  resist  abrasion  if  held  securely  in  place.  In 
an  asphalt  pavement  they  are  held  by  the  asphalt  and  a  wearing 
surface  of  great  resistance  to  abrasion  results.  In  a  sand-clay 
road  they  are  bound  together  by  clay  in  a  less  firm  manner  but 
one  giving  excellent  results  on  well-drained  roads  carrying  light 
traffic.  The  aim  of  the  builder  of  such  a  road  is  to  employ  just 
enough  of  the  stickiest  clay  at  his  command  to  fill  the  pores  of 
the  sand  and  to  mix  these  materials  together  so  thoroughly  that 
there  are  neither  lumps  of  clay  nor  pockets  of  loose  sand  left  in 
the  surfacing.  This  gives  the  maximum  amount  of  hard  sand 
to  carry  the  traffic  and  the  minimum  amount  of  clay  to  bind  it. 
More  sand  makes  a  less  durable  road  and  more  clay  makes  one 
which  becomes  soft  more  rapidly  when  wet. 

There  is  a  great  difference  in  the  value  of  different  clays  for 
such  work.  Some  of  them  become  dough-like  when  mixed  with 
a  certain  amount  of  water  and  can  be  molded  into  objects  which 
retain  their  shape  after  drying.  If  these  molded  objects  are  im- 
mersed in  water  they  will  retain  their  form  for  a  long  time.  These 
varieties  are  called  "plastic  clays"  and  the  most  plastic  are 
called  "ball  clays."  There  are  other  varieties  which  fall  to  pieces 
more  or  less  quickly  when  wet,  as  quicklime  does,  and  they  are 
therefore  called  "slaking  clays."  They  are  more  easily  mixed 
with  sand  than  the  plastic  clays  but  they  have  much  less  bind- 
ing power  and  a  road  built  with  them  is  less  durable  when  dry 
and  more  easily  rutted  when  wet.  The  amount  of  clay  to  be  used 
can  be  determined  by  a  simple  field  test  described  as  follows 
by  Andrew  P.  Anderson: 

From  typical  samples  of  each  of  the  available  clays,  test  mixtures, 
varying  by  one-half  part,  are  made  with  the  sand  so  that  each  clay  is  rep- 
resented by  a  set  of  mixtures  ranging  by  successive  steps  from  one  part 
sand  and  three  parts  clay  to  four  parts  sand  and  one  part  clay.  These 
are  worked  up  with  water  into  a  putty-like  mass  and  from  each  mix 
two  equal  quantities  are  taken  and  rolled  between  the  palms  of  the  hands 
into  reasonably  true  spheres,  labeled  and  placed  in  the  sun  to  dry.  When 
thoroughly  baked,  a  set  of  spheres  representing  any  one  clay  is  placed  in 
a  flat  pan  or  dish  and  enough  water  poured  gently  into  the  pan  to  cover 
them,  care  being  taken  not  to  pour  the  water  directly  on  the  samples.  Some 
samples  will  begin  to  disintegrate  immediately.  Those  breaking  dowo 


48  AMERICAN  HIGHWAY  ASSOCIATION 

most  slowly  contain  most  nearly  the  proper  proportion  of  sand  and  clay 
for  the  particular  materials.  The  relative  binding  power  of  the  various 
clays  may  then  be  determined  by  comparing  the  hardness  and  resistance 
to  abrasion  of  the  various  dry  samples  having  the  correct  proportion  of 
sand  and  clay,  as  determined  by  the  water  tests. 

In  February,  1917,  representatives  of  21  state  highway  depart- 
ments and  of  the  U.  S.  Office  of  Public  Roads  recommended  the 
following  mixtures  for  hard,  medium  and  soft  classes  of  sand-clay 
roads. 

Hard  class:  Clay,  9  to  15  per  cent;  silt,  5  to  15  per  cent;  total 
sand  65  to  80  per  cent;  sand  retained  on  a  60-mesh  sieve,  45  to 
60  per  cent. 

Medium  class:  Clay,  15  to  25  per  cent;  silt,  10  to  20  per  cent; 
total  sand,  60  to  70  per  cent;  sand  retained  on  a  60-mesh  sieve, 
30  to  45  per  cent. 

Soft  class:  Clay,  10  to  25  per  cent;  silt,  10  to  20  per  cent; 
total  sand,  55  to  80  per  cent;  sand  retained  on  a  60-mesh  sieve, 
15  to  30  per  cent. 

By  clay  is  meant  material  separated  by  subsidence  through  water 
and  possessing  plastic  or  adhesive  properties ;  it  is  generally  below 
0.01  mm.  in  diameter.  By  silt  is  meant  the  fine  material  other 
than  clay  which  passes  a  200-mesh  sieve  and  is  generally  from  0.07 
to  0.01  mm.  in  diameter.  By  sand  is  meant  the  hard  material 
which  passes  a  10-mesh  sieve  and  is  retained  on  a  200-mesh  sieve, 
and  is  generally  from  1.85  to  0.07  mm.  in  diameter. 

The  larger  part  of  the  following  explanation  of  the  construc- 
tion of  sand-clay  roads  was  prepared  by  W.  S.  Keller,  State 
engineer  of  Alabama,  where  many  miles  of  sand-clay  roads  have 
been  built  and  are  giving  good  satisfaction: 

Every  farmer  who  lives  in  a  section  of  country  where  both  sand  and 
clay  are  prevalent,  is  more  than  likely  traveling  over  a  section  of  natural 
sand-clay  road  but  is  ignorant  of  the  fact.  He  can  call  to  mind  some 
particular  spot  on  the  road  he  travels,  though  it  may  not  be  more  than  100 
feet  in  length,  that  is  always  good  ana  rarely  requires  the  attention  of  the 
road  hands.  Good  drainage  will  be  noticed  at  this  place  and  if  he  takes 
the  trouble  to  investigate,  he  will  find  that  a  good  mixture  of  sand  and 
clay  forms  the  wearing  surface.  If  this  100  feet  of  road  is  always  good 
then  the  entire  road  can  be  made  like  it  provided  man  will  take  advantage 
of  the  lesson  taught  by  nature  and  grade  the  road  so  that  the  drainage 
will  be  good  and  surface  the  balance  of  the  road  with  the  same  material. 
If  it  is  not  possible  to  find  this  ready  mixed  surfacing  material  convenient 
to  the  road  it  may  be  possible  to  find  the  two  ingredients  in  close  proximity. 
In  case  the  road  after  grading  shows  an  excess  of  sand,  clay  should  be 
added,  or  in  case  clay  predominates,  sand  should  be  added  to  produce 
good  results.  There  are  four  general  ways  in  which  sand-clay  roads  may 
be  built: 

1.  Ready  mixed  sand  and  clay  placed  on  clay,  sand  or  ordinary  foun- 
dation. 

2.  Sand  and  olay  placed  on  soil  foundation  and  mixed. 


EARTH  AND  SAND-CLAY  ROADS  49 

3.  Clay  hauled  on  a  sand  foundation  and  mixed  with  the  sand. 

4.  Sand  hauled  on  a  clay  foundation  and  mixed  with  the  clay. 
Taking  up  the  various  methods  in  order: 

1.  A  natural  mixture  of  sand  and  clay  can  often  be  found  where  the 
two  materials  are  found  separate.  The  most  important  point  is  to  know 
the  natural  mixture  when  seen.  The  very  best  guide  to  this  is  to  find  a 
natural  piece  of  good  road.  A  sample  from  the  best  of  this  good  section 
will,  by  comparison,  indicate  what  is  required,  close  to  the  road  to  be  sur- 
faced. This  natural  mixture  of  sand  and  clay  can  be  noticed  where  red 
clay  and  sand  crop  out,  usually  well  up  in  the  hills,  having  in  ditches  and 
cuts  the  appearance  of  red  sandstone.  A  good  stratum  of  well  mixed 
sand  and  clay  will  otand  perpendicular  in  cuts  and  ditches,  resisting  ero- 
sion almost  as  well  as  sandstone.  A  test  of  the  best  natural  sand-clay 
mixtures  will  show  the  sand  forms  about  70  per  cent  of  the  whole.  The 
test  is  very  simple.  Take  an  ordinary  medicine  glass,  measure  2  ounces 
of  the  mixture  into  the  glass  and  wash  out  the  clay.  Dry  the  remaining 
sand  and  measure  again  on  the  medicine  glass.  The  loss  will  be  the  amount 
of  clay  originally  contained  in  the  mass. 

Before  placing  any  sand-clay  on  the  road,  the  road  should  be  graded 
to  the  desired  width.  The  surface  of  the  graded  road  should  be  flat  or 
slightly  convex.  The  sand-clay  should  be  put  on  from  8  to  12  inches  in 
thickness,  depending  on  the  character  of  the  subgrade  or  foundation. 
With  a  hard  clay  for  foundation,  8  inches  of  sand  clay  will  suffice.  If  the 
subgrade  is  sand  it  is  well  to  put  on  as  much  as  12  inches  of  the  surfacing 
material.  After  a  few  hundred  feet  of  surfacing  material  has  been  placed, 
a  grading  machine  should  be  run  over  it  to  smooth  and  crown  the  road 
surface  before  the  top  becomes  hard  and  resists  the  cutting  of  the  blade. 
It  is  a  good  plan  to  turn  the  blade  of  the  machine  so  as  to  trim  the  edges 
of  the  surface  part,  discharging  the  excess  sand  and  clay  onto  the  earth 
shoulders.  After  one  round  trip  with  the  blade  turned  out,  the  remaining 
dress  work  with  the  machine  should  be  with  the  blade  turned  in,  with  the 
exception  of  one  trip  down  the  center  of  road  with  the  blade  at  right  angles 
to  the  axis  of  the  road  for  the  purpose  of  distributing  any  excess  of  mate- 
rial left  in  the  center. 

After  the  machine  work,  it  is  well  to  follow  with  a  drag,  which  smooths 
any  rough  places  left  by  the  machine  and  leaves  the  road  with  a  smooth, 
even  surface.  A  sand-clay  road,  unlike  other  roads,  cannot  be  finished 
in  a  short  space  of  time.  It  can  be  left  in  an  apparently  finished  condi- 
tion with  a  hard  smooth  surface,  but  it  will  be  found  on  close  examina- 
tion that  the  hard  surface  is  in  reality  only  a  crust,  below  which  there  are 
several  inches  of  loose  material.  After  the  first  hard  rain  the  crust  soft- 
ens, the  road  becomes  bad  and  the  work  appears  to  be  a  failure.  This, 
however,  is  just  what  is  needed  to  make  it  eventually  good.  After  the 
surface  has  dried  until  the  mass  is  in  a  plastic  state,  it  should  be  dragged 
until  the  surface  is  once  more  smooth,  with  proper  crown,  and  should  be 
kept  this  way  by  dragging  at  least  once  a  day  until  the  sun  has  baked  it 
hard  and  firm.  The  mistake  of  keeping  traffic  off  during  this  process  of 
resetting  should  not  be  made.  The  continuous  tamping  of  the  wheels  of 
wagons  and  hoofs  of  horses  is  just  what  is  needed  to  compact  the  sand- 
clay  into  a  homogeneous  mass.  The  ordinary  roller  is  not  very  effective 
in  this  work,  but  corrugated  rollers  have  given  excellent  results.  One 
type  which  is  widely  used  has  18  cast-iron  wheels  weighing  300  pounds 
each,  which  compress  the  bottom  of  the  mixture  first.  As  the  material 
becomes  more  and  more  compact  the  wheels  ride  higher  and  higher  and 
finally  the  surface  is  so  hard  that  the  roller  does  not  sink  into  it  at  all.  A 
drag  is  an  indispensable  machine  in  the  construction  of  any  kind  of  sand- 
olay  road. 


50  AMERICAN   HIGHWAY  ASSOCIATION 

2.  Sand  and  clay  placed  on  a  soil  foundation  and  mixed.     This  is  nec- 
essary where  the  old  road  has  neither  a  sand  nor  clay  foundation  and  it 
is  impossible  to  find  the  two  ingredients  ready  mixed,  but  possible  to  get 
both  in  separate  state  near  at  hand.     The  clay  should  first  be  placed 
on  the  road  to  a  depth  of  4  inches  and  the  required  width.     It  is  not 
wise  to  place  more  than  a  few  hundred  lineal  feet  of  clay  before  the 
sand  is  hauled,  as  the  clay  rapidly  hardens  and  makes  the  mixing  process 
difficult.     After,  say,  400  feet  of  clay  has  been  placed,  the  clay  should  be 
broken  by  means  of  a  plow  and  harrow,  if  it  has  become  hard,  and  sand  to 
a  depth  of  6  inches  placed  on  it.     This  should  be  plowed  and  harrowed  in 
thoroughly.     This  is  best  done  immediately  following  a  rain,  as  the  two 
can  be  more  satisfactorily  mixed.     The  traffic  aids  the  mixing  and  should 
be  encouraged  on  the  road.    After  the  mass  appears  to  be  well  mixed,  the 
road  should  be  properly  shaped,  as  previously  explained.     The  road  should 
be  given  watchful  attention  and  should  sand  or  mud  holes  appear,  a  second 
plowing  and  mixing  should  be  given  it. 

3.  Clay  hauled  on  a  sand  foundation  and  mixed  with  the  sand.     The 
mixing  process  is  similar  to  that  described  under  second  head.     It  is  only 
necessary  to  add  that  as  the  foundation  is  sand,  a  little  more  clay  will  be 
necessary  than  where  the  foundation  is  of  clay  or  soil. 

4.  Sand  hauled  on  a  clay  foundation  and  mixed  with  clay.     The  clay 
foundation  should  be  plowed  to  a  depth  of  4  inches  and  harrowed  with  a 
disk  or  tooth  harrow  until  the  lumps  are  thoroughly  broken  or  pulver- 
ized.   Sand  should  then  be  added  to  a  depth  of  6  inches  and  mixed  as  be- 
fore described. 

Sand  and  clay  can  be  mixed  best  when  wet,  but  as  most  road  construc- 
tion is  done  in  the  summer  months,  it  is  necessary  to  do  most  of  the  mix- 
ing dry  and  keep  the  road  in  shape  after  the  first  two  or  three  rains,  while 
the  passing  wagons  and  vehicles  give  the  road  a  final  wet  mixing.  A  sand- 
clay  road  is  the  cheapest  road  to  maintain,  for  the  reason  that  it  can  be 
repaired  with  its  own  material.  With  a  drag  or  grading  machine  ruts 
can  be  filled  with  material  scraped  from  the  edges,  whereas  on  gravel  or 
macadam  roads,  this  is  not  possible.  The  repairing  of  these  roads  can  be 
done  almost  exclusively  with  the  drag,  only  enough  hand  work  being  re- 
quired to  keep  the  gutters  open  and  the  growth  of  weeds  cut  on  the  should- 
ers. Holes  are  repaired  by  adding  more  sand-clay,  and  when  many  of  them 
appear  fresh  sand-clay  should  be  spread  over  the  surface  of  the  road.  If 
the  road  gets  into  really  bad  condition,  the  roadbed  should  be  plowed  up, 
reshaped  and  fresh  sand-clay  added.  This  is  unnecessary  where  the  road 
is  maintained  properly  and  the  travel  is  not  too  heavy  for  the  type  of 
construction. 


GRAVEL  ROADS1 

At  the  close  of  1914,  45  per  cent,  of  the  surfaced  roads  in  the 
United  States  were  gravel  roads,  as  shown  in  detail  in  a  table  in 
Part  III  of  this  volume.  The  presence  of  good  gravel  in  many 
parts  of  the  country  and  the  low  cost  of  constructing  and  main- 
taining gravel  roads  will  make  them  a  leading  type  for  many 
years  to  come. 

Some  gravels  are  much  better  for  road  construction  than 
others.  In  Michigan,  where  three-fifths  of  the  surfaced  roads 
are  built  of  gravel,  the  value  of  this  material  for  the  purpose 
is  held  to  vary  with  the  percentage  of  pebbles  in  it,  the  road- 
building  value  of  the  rock  of  which  the  pebbles  are  composed, 
and  the  cementing  properties  of  the  fine  material  mixed  with  the 
pebbles.  In  this  State  at  least  60  per  cent  by  weight  of  the 
gravel  for  state  reward  roads  must  be  pebbles  larger  than  J-inch. 
No  pebbles  larger  than  2J  inches  are  used  in  the  bottom  of  the 
road  and  none  larger  than  1J  inches  in  the  top.  The  binder 
required  for  holding  the  pebbles  together  is  clay,  uniformly  mixed 
with  the  pebbles,  free  from  lumps,  and  amounting  to  not  over 
10  per  cent  of  the  total  weight  of  the  gravel. 

There  is  a  large  mileage  of  gravel  roads  in  New  Jersey,  and 
as  a  result  of  experience  with  them,  the  State  highway  depart- 
ment rejects  gravel  with  over  5  per  cent  retained  on  a  Ij-inch 
circular  opening  and  over  35  per  cent  retained  on  a  ^-inch  cir- 
cular opening.  Three  grades  are  recognized.  Grade  A  is  a 
pebble  gravel  with  a  clay  binder  with  not  less  than  25  nor  more 
than  35  per  cent  retained  on  a  J-inch  circular  opening,  not  less 
than  40  nor  more  than  60  per  cent  retained  on  a  10-mesh  sieve, 
not  less  than  8  nor  more  than  20  per  cent  passing  a  200-mesh 
sieve,  and  the  balance  a  fairly  well  graded  sand.  Grade  B  is  a 
sandy  gravel  depending  upon  oxide  of  iron  for  its  cementing 
properties,  with  20  to  40  per  cent  retained  on  a  10-mesh  sieve 
and  10  to  25  per  cent  passing  a  200-mesh  sieve.  Of  this  material 
passing  a  200-mesh  sieve,  at  least  40  per  cent  must  be  soluble 
in  a  1:3  dilution  of  hydrochloric  acid.  Grade  C  is  gravel  which 
does  not  fall  under  either  of  the  previously  mentioned  grades  but 
is  approved  by  the  engineer  for  the  bottom  part  of  gravel  roads. 

1  Revised  by  Frederic  E.  Everett,  State  Highway  Commissioner  of  New 
Hampshire. 

51 


52  AMERICAN  HIGHWAY  ASSOCIATION 

In  Illinois,  the  State  highway  department  requires  the  gravel 
to  be  rather  uniformly  graded  in  size  from  fine  material  to  peb- 
bles that  will  just  pass  a  3^-inch  ring,  and  not  over  15  per  cent 
of  the  mass  (exclusive  of  clay)  passing  a  f-inch  ring.  It  must 
not  contain  over  5  per  cent  of  loam  but  it  must  have  15  to  25 
per  cent  of  clay  by  dry  measure.  If  a  local  gravel  does  not  form 
a  good  bond,  the  contractor  must  supply  a  bonding  gravel  for  the 
top  f-inch  of  the  road.  All  of  this  material  must  pass  a  1-inch 
screen  and  contain  40  per  cent  of  pebbles  retained  on  a  J-inch 
screen  and  from  20  to  30  per  cent  of  clay  and  loam,  not  more 
than  5  per  cent  being  loam. 

The  variations  in  these  specifications  show  the  range  of  prop- 
erties of  the  materials  found  useful  by  experience.  Few  attempts 
have  been  made  to  prepare  a  general  specification  for  road  gravel 
on  this  account.  The  following  requirements  were  adopted  by  the 
American  Society  of  Municipal  Improvements  in  1916  and  re- 
commended by  the  Committee  on  Materials  for  Road  Con- 
•struction  of  the  American  Society  of  Civil  Engineers: 

Two  mixtures  of  gravel,  sand  and  clay  shall  be  used,  hereinafter  desig- 
nated in  these  specifications  as  No.  1  product  (for  top  course)  and  No.  2 
product  (for  middle  and  bottom  courses.) 

No.  1  product  shall  consist  of  a  mixture  of  gravel,  sand  and  clay,  with 
the  proportions  of  the  various  sizes  as  follows:  All  to  pass  a  1^-inch  screen 
and  to  nave  at  least  60  and  not  more  than  75  per  cent  retained  on  a  J-inch 
screen;  at  least  25  and  not  more  than  75  per  cent  of  the  total  coarse  aggre- 
gate (material  over  i-inch  in  size)  to  be  retained  on  a  f-inch  screen;  at 
least  65  and  not  more  than  85  per  cent  of  the  total  fine  aggregate  (mate- 
rial under  J  inch  in  sizo)  to  be  retained  on  a  200-mesh  sieve. 

No.  2  product  shall  consist  of  a  mixture  of  gravel,  sand  and  clay,  with 
the  proportions  of  the  various  sizes  as  follows :  All  to  pass  a  2 J-inch  screen 
and  to  have  at  least  60  and  not  more  than  75  per  cent  retained  on  a  J-inch 
screen;  at  least  25  and  not  more  than  75  per  cent  of  the  total  coarse  aggre- 
gate to  be  retained  on  a  1-inch  screen;  at  least  65  and  not  more  than  85 
per  cent  of  the  total  fine  aggregate  to  be  retained  on  a  200-mesh  sieve. 

It  is  evident  that  the  most  useful  information  concerning  the 
value  of  any  gravel  for  road  work  is  obtained  by  examining  a 
road  built  of  it.  If  there  is  a  good  gravel  road  and  the  source 
of  this  gravel  is  not  known,  a  sample  of  the  gravel  can  be  analyzed 
mechanically  by  a  portable  sand  tester,  and  the  gravel  deposits 
in  the  vicinity  tested  by  the  same  instrument  until  one  is  found 
showing  about  the  same  properties.  An  exact  agreement  should 
not  be  expected.  Tests  of  the  gravel  in  a  satisfactory  road  in 
the  State  of  Washington  and  of  the  material  in  the  pit  from 
which  it  was  obtained  gave  the  following  variations: 


GRAVEL   ROADS 


53 


Mechanical  Analyses  of  Identical  Gravel  Sampled  at  Pit  and  in  the  Road 


PASSING 

PIT 

ROAD 

PASSING 

PIT 

ROAD 

PASSING 

PIT 

ROAD 

200  sieve 
100  sieve 
80  sieve 
50  sieve 
40  sieve 

per  cent 

4.1 
8.0 
6.6 
16.3 
13.1 

per  cent 

6.4 
8.1 
4.7 
7.4 
6.9 

30  sieve 
20  sieve 
10  sieve 
8  sieve 
4  sieve 

per  cent 

10.2 
14.7 
14.5 
2.6 
5.2 

per  cent 

6.5 
12.1 
12.7 
3.4 
9.5 

2  sieve 
f  inch 
1  inch 
1J  inch 
1?  inch 

per  cent 

3.5 
1.2 

j*r  cent 

8.3 
5.7 
1.9 
6.4 

Where  coarse  gravel  is  composed  of  rock  pebbles  giving  a 
cementitious  powder  some  engineers  consider  it  unwise  to  use 
enough  clay  binder  to  fill  the  voids.  If  roads  of  coarse  gravel 
bound  with  a  large  amount  of  clay  are  used  by  many  automobiles 
the  pebbles  become  dislodged  and  the  road  does  not  become  hard, 
it  is  claimed.  Consequently  these  engineers  prefer  to  use  a 
smaller  amount  of  clay  and  to  allow  the  traffic  to  wear  down  the 
road  and  produce  the  necessary  binder  by  attrition  and  internal 
disintegration  of  the  mass  of  gravel.  This  process  makes  it  neces- 
sary to  maintain  the  road  carefully  for  some  time  after  its  com- 
pletion, but  is  stated  to  give  a  better  road  eventually  with  some 
classes  of  gravel. 

In  New  England,  where  gravel  roads  have  been  built  extensive- 
ly, it  is  generally  considered  safe  to  use  on  roads  for  light  traffic 
the  gravel  from  any  pit  where  the  face  stands  vertical  and  has 
to  be  loosened  before  it  can  be  shoveled.  Other  gravels  usually 
have  to  be  supplied  with  a  binder.  It  is  always  desirable  to  make 
a  careful  search  for  all  deposits  of  gravel  and  an  examination 
of  the  quality  of  each  before  deciding  upon  the  deposit  to  use. 
In  Dubuque  County,  Iowa,  for  instance  several  months  were 
spent  in  such  an  investigation  because  the  local  limestone  was 
too  soft  for  road  use.  Finally  a  satisfactory  pit  was  found  1J 
miles  from  the  road  to  be  improved,  and  by  transporting  it  on 
a  light  narrow-gauge  railway  :to  the  road  and  then  distributing 
it  by  branches  of  this  railway  and  by  motor  trucks  and  dump 
wagons,  its  cost  on  the  road  was  kept  down  to  a  satisfactory 
figure. 

Preparing  the  Gravel 

The  management  of  the  gravel  pit  should  receive  enough  study 
and  attention  to  make  sure  that  the  material  is  delivered  to  the 
wagons  or  cars  at  the  lowest  cost.  The  organization  for  the 
purpose  will  depend  upon  the  location  of  the  pit,  the  quality  of 
the  gravel  and  the  quantity  of  material  to  be  taken  out.  Where 
there  is  only  a  small  percentage  of  the  gravel  which  is  over  size, 


54  AMERICAN   HIGHWAY   ASSOCIATION 

and  the  remainder  runs  a  uniformly  good  mixture,  the  large 
stones  can  be  removed  by  a  flat  gravel  screen,  or,  on  small  works, 
can  be  forked  out  during  loading.  It  is  not  always  necessary  to 
go  to  the  expense  of  screening.  With  a  good  foreman  in  the  pit 
it  may  be  possible  to  get  a  proper  mixture  of  the  material  from 
a  pit  where  the  gravel  lies  in  strata  of  different  sized  pebbles, 
provided  there  is  also  a  good  foreman  on  the  road,  so  that  the 
strippings,  if  any,  will  be  placed  on  the  shoulders  and  the  over- 
large  material  will  be  used  for  foundations  in  low  places. 

Where  there  is  a  considerable  proportion  of  overlarge  stone 
in  the  gravel  it  is  customary  to  set  up  a  crushing  and  screening 
plant  at  the  pit.  For  example,  Kane  County,  Illinois,  has  an 
outfit  consisting  of  a  jaw  crusher,  screen,  elevator  and  storage 
bin  holding  15  cubic  yards.  The  gravel  is  first  screened,  because 
by  taking  out  the  material  of  suitable  size  for  road  work  only  the 
large  stone  is  fed  to  the  crusher  and  its  capacity  is  thereby  much 
increased.  The  presence  of  the  small  stone  in  the  crusher  tends 
to  clog  it  and  retard  the  breaking  of  the  large  stone.  The  screened 
and  crushed  material  is  discharged  by  gravity  from  the  bins  into 
the  5-yard  motor  trucks  which  are  used  for  delivering  it.  The 
pit  material  is  delivered  to  the  screen  by  a  belt  conveyor,  18 
inches  wide  and  40  feet  long.  One  end  of  the  belt  is  under  a  plat- 
form having  a  hopper  over  the  belt.  The  gravel  is  brought  by 
slip  scrapers  to  the  platform  and  dumped  through  the  hopper 
onto  the  conveyor. 

In  some  plants  of  this  character  the  gravel  is  run  over  a  bar 
screen  or  "grizzly"  which  holds  back  all  oversize  stone  and  delivers 
it  to  the  crusher.  This  keeps  the  large  stone  entirely  out  of  the 
screen.  In  Wisconsin  work  the  screen  has  $-inch  perforations 
for  the  first  half  of  its  length  and  If -inch  perforations  for  the 
second  half,  giving  three  sizes  of  gravel.  The  jaws  of  the  crusher 
are  set  to  give  about  equal  parts  of  the  two  coarser  sizes  separated 
by  the  screen. 

As  the  pebbles  composing  gravel  are  rounded  and  do  not  lock 
together  as  well  as  broken  stone,  it  is  customary  to  use  somewhat 
smaller  sizes  of  gravel  than  of  crushed  stone.  Gravel  obtained  from 
beaches  and  rivers  is  usually  more  rounded  than  that  from  pits 
and  consequently  may  not  be  so  good  for  roads,  unless  suitable 
binding  gravel  can  be  used  for  a  wearing  surface  or  limestone 
screenings  or  other  good  binding  material  can  be  used  with  it. 

Pit-run  Gravel  Roads 

Many  miles  of  gravel  roads  have  been  built  by  dumping  the 
gravel  on  the  roadbed,  spreading  it  roughly  and  allowing 
traffic  to  consolidate  it.  The  consolidation  is  a  tedious  process, 


GRAVEL  ROADS 


55 


but  good  roads  often  result  in  the  end,  particularly  if  the  road 
is  kept  well  dragged  so  that  ruts  and  holes  are  prevented.  Bet- 
ter results  are  obtained,  however,  if  the  gravel  is  rolled  after  it 
is  spread.  The  loads  of  large  stone  should  be  dumped  at  the  low 
or  soft  places  on  the  roadbed.  In  deep,  mealy  sand,  the  sub- 
grade  is  sometimes  covered  with  marsh  hay,  wet  sand  or  fine 

Cubic  Yards  of  Loose  Gravel  Required  to  make  One  Mile  of  Road  of  Dif- 
ferent Widths  and  Thicknesses.  Based  on  Table  of  Commissioner  of  Pub- 
lie  Roads  of  New  Jersey. 


WIDTH 

THICKNESS   OF  ROAD   AFTER   CONSOLIDATION,   INCHES 

0 

7 

8 

9 

10 

11 

12 

feet 

6 

880 

,027 

1,173 

1,320 

1,467 

1,613 

1*760 

7 

1,027 

,198 

1,369 

1,540 

1,711 

1,882 

2,054 

8 

1,173 

,369 

1,564 

1,760 

1,956 

2,151 

2,346 

9 

1,320 

,540 

1,760 

1,980 

2,200 

2,420 

2,640 

10 

1,467 

,711 

1,956 

2,200 

2,444 

2,689 

2,934 

11 

1,613 

,882 

2,151 

2,420 

.2,689 

2,958 

3,226 

12 

1,760 

2,053 

2,346 

2,640 

2,933 

3,227 

3,520 

13 

1,807 

2,224 

2,542 

2,860 

3,178 

3,496 

3,614 

14 

2,054 

2,396 

2,738 

3,080 

2,422 

3,764 

4,108 

15 

2,200 

2,567 

2,933 

3,300 

3,667 

4,033 

4,400 

16 

2,346 

2,738 

3,128 

3,520 

3,912 

4,302 

4,692 

17 

2,493 

2,909 

3,324 

3,740 

4,156 

4,571 

4,986 

18 

2,640 

3,080 

3,520 

3,960 

4,400 

4,840 

5,280 

19 

2,787 

3,250 

3,716 

4,180 

4,644 

5,109 

5,574 

20 

2,933 

3,422 

3,912 

4,400 

4,888 

5,378 

5,866 

Cubic  Yards  of  Crushed  Stone  or  Gravel  Required  to  Give  Different  Depths 
when  Lying  Loose  on  One  Mile  of  Roadways  of  Different  Widths.  Based 
on  Table  of  Wisconsin  Highway  Commission. 


DEPTH   OF  LOOSE   MATERIAL,  INCHES 


SURFACE 

1 

ii 

ti 

2 

3 

4 

5 

6 

feet 

cu.  yds. 

cu.  yds. 

cu.  yds. 

cu.  yds. 

cu.  yds. 

cu.  yds. 

cu.  yds. 

cu.  yds. 

8 

130 

160 

195 

260 

391 

521 

652 

782 

9 

147 

180 

220 

294 

440 

587 

734 

880 

10 

163 

200 

244 

326 

489 

652 

816 

977 

12 

196 

240 

293 

392 

587 

783 

980 

1,171 

14 

218 

280 

342 

436 

684 

913 

1,141 

1,369 

15 

244 

300 

366 

488 

733 

979 

1,222 

1,466 

16 

261 

325 

391 

522 

782 

1,043 

,304 

1,565 

18 

294 

367 

440 

588 

880 

1,174 

,468 

1,760 

20 

326 

400 

488 

652 

978 

1,304 

,632 

1,954 

22 

359 

440 

537 

718 

1,076 

1,434 

,796 

2,148 

24 

392 

480 

584 

784 

1,174 

1,564 

,960 

2,342 

56 


AMERICAN  HIGHWAY   ASSOCIATION 


Weight  in  Pounds  Per  Cubic  Yard  of  Sand  and  Gravel.    From 
Resources  of  the  United  States,  1915." 


'Mineral 


BTATB 

o 
E 

•4 

OB 

ORAVEL 

STATE 

a 

5 

GRAVEL 

STATE 

a 

03 

3 

« 
o 

Alabama  
California  
Florida  

2505 
2645 
2605 
2820 
2700 
2720 
2580 

2790 

2895 
2680 
3005 
2945 
2850 
2830 

Massachusetts 
Michigan  
Minnesota  
Missouri  
New  Jersey.  .  . 
New  York  .... 
Ohio.  . 

2710 
2895 
2865 
2680 
2600 
2590 
2700 

2810 

2985 
2880. 
2840 
2730 
2760 
2830 

Oregon..  . 

2620 
2500 
2695 
2930 
2570 
2800 
2665 

2880 
2680 
2910 
3065 
2780 
2970 
2820 

Pennsylvania 
Texas  
Washington.  . 
W.Virginia.. 
Wisconsin...  . 
Average.. 

Illinois.. 

Indiana.  . 

Iowa..  . 

Kentucky  

NOTE:  The  average  weights  were  obtained  from  670  producers  of  sand 
and  560  producers  of  gravel  in  all  parts  of  the  country;  the  range  was 
from  2200  to  4000  pounds  for  sand  and  from  2200  to  4200  pounds  for  gravel. 
The  weights  given  for  each  state  are  the  averages  of  the  reports  from  ten 
or  more  producers  in  that  State. 

brush  to  hold  the  gravel.  The  stone  should  be  well  raked  and 
no  stone  larger  than  2  inches  should  be  allowed  in  the  top  of  the 
road. 

It  is  best  to  lay  the  gravel  in  two  courses,  each  5  or  6  inches 
thick  when  loose.  The  spreading  of  the  first  course  begins  at  the 
place  on  the  road  where  the  gravel  reaches  it  and  in  this  way 
the  material  is  consolidated  by  the  teaming  over  it.  When  this 
is  very  hard  work  enough  clay  is  sometimes  added  to  pack  the 
gravel.  Some  engineers  require  this  course  to  be  harrowed. 
It  is  desirable  to  shape  this  course  with  a  grading  machine  and 
roll  it,  but  if  the  equipment  is  not  available  it  can  be  improved 
by  using  a  drag  or  a  road  plane,  as  described  on  page  266. 

After  a  considerable  stretch  of  the  bottom  course  has  been 
finished,  the  second  course  can  be  started,  beginning  at  the  end 
farthest  from  the  gravel  pit,  so  as  to  have  the  teaming  do  as  much 
consolidation  work  on  the  bottom  course  as  possible.  Some 
engineers  require  the  entire  bottom  course  to  be  finished  before 
the  second  is  started.  It  is  best  to  harrow  the  second  course  be- 
cause pit-run  gravel  usually  needs  good  mixing  and  the  harrow 
will  bring  the  large  stones  to  the  surface,  so  they  can  be  thrown 
aside.  If  the  gravel  needs  a  binder  the  harrowing  will  help  to 
distribute  it  evenly.  If  too  much  clay  is  added  the  road  is  likely 
to  rut  in  wet  weather  and  be  dusty  in  dry  weather.  After  the  har- 
rowing, the  surface  is  shaped  with  a  grader,  if  one  is  available,  or 
with  a  drag  or  plane.  It  should  then  be  rolled,  and  with  some 
gravel  the  rolling  gives  the  best  results  if  the  road  is  first  wet. 

Gravel  is  a  surfacing  material,  it  will  not  make  a  defective 
roadbed  good,  although  it  may  temporarily  improve  it.  Con- 


GRAVEL   ROADS  57 

sequently  it  is  best  to  allow  a  new  roadbed  to  be  used  as  an  earth 
road  for  a  year,  so  it  will  have  a  chance  to  settle.  If  it  is  kept 
well  dragged  during  this  seasoning  period,  it  will  become  hard 
enough  to  sustain  the  gravel.  If  it  is  known  that  gravel  will  be 
placed  after  a  year's  use,  the  earth  road  should  be  dragged  to  a 
very  flat  crown,  in  order  to  prevent  too  much  crown  in  the  gravel 
road.  When  gravel  must  be  placed  on  a  fresh  roadbed,  it  is 
sometimes  advisable  to  lay  a  6-inch  course  and  allow  that  to 
become  consolidated  by  traffic  before  the  second  course  is  laid. 
If  there  are  any  defects  in  the  roadbed  they  will  become  apparent 
during  the  early  use  of  the  road  and  can  be  repaired  before  the 
completion  of  the  surfacing.  If  only  the  bottom  course  is  laid 
the  first  season  it  should  be  well  dragged,  for  inequalities  in  the 
bottom  course  are  usually  reproduced  in  the  upper  course,  no 
matter  how  carefully  the  latter  is  laid  and  shaped. 

There  are  two  methods  of  placing  gravel.  That  usually  em- 
ployed on  pit-run  gravel  roads  is  called  the  feather-edge  method. 
The  roadbed  to  receive  the  gravel  is  graded  to  a  very  small  crown 
and  the  gravel  is  spread  on  it  to  a  nearly  uniform  thickness  until 
within  about  12  inches  of  the  edge,  when  the  bed  is  sloped  off  to 
a  mere  row  of  pebbles  at  the  edge.  In  the  second  method  of  con- 
struction, a  shallow  trench,  sometimes  called  a  "gravel  bed" 
or  a  "box,"  is  excavated  in  the  top  of  the  roadbed,  and  the  gravel 
deposited  in  it.  If  it  rains  this  trench  is  likely  to  become  muddy 
and  to  prevent  this  drainage  channels  should  be  cut  through 
the  shoulders  to  the  side  ditches.  Bank  gravel  will  become  con- 
solidated and  shed  water  more  quickly  than  stream  gravel  and 
it  is  better  suited  for  the  trench  method  in  consequence.  The 
feather-edge  method  is  less  expensive  and  more  easily  carried 
on  if  traffic  must  be  permitted  on  the  road  during  construction. 

The  following  explanation  of  the  construction  of  a  two-course 
feather-edge  gravel  road  was  written  by  H.  E.  Bilger,  road  engi- 
neer of  the  Illinois  Highway  Department: 

When  the  bonding  material  in  the  gravel  is  not  entirely  satisfactory 
with  respect  to  both  quality  and  quantity,  it  is  usually  advisable  that 
two-course  construction  be  adopted.  Whether  or  not  the  work  is  to  be 
done  by  contract,  it  is  important  that  there  be  used  some  positive  and 
accurate  method  of  determining  the  volume  of  gravel  delivered  upon  the 
roadbed.  There  are  several  methods  by  which  this  can  be  accomplished, 
but  experience  seems  to  indicate  that  by  the  use  of  temporary  side- 
board forms  the  desired  results  can  be  assured  and  this  method  is  not 
uneconomical. 

Upon  the  satisfactory  completion  of  the  roadbed  there  should  be  set 
thereon,  true  to  line  and  grade,  temporary  side  forms  having  a  width 
equal  to  the  depth  of  the  loose  gravel,  which  should  be  shown  on  the  plans. 
These  boards  should  be  held  in  place  by  stakes  at  such  intervals  as  will 
prevent  lateral  deflection  greater  than  about  3  inches  from  the  true  align- 
ment. Whether  the  gravel  is  hauled  by  wagons,  motor  trucks,  industrial 


58  AMERICAN   HIGHWAY   ASSOCIATION 

railways,  or  other  vehicles,  it  may  be  dumped  directly  upon  the  subgrade. 
After  there  has  been  placed  upon  the  subgrade  a  sufficient  quantity  of 
gravel  for  the  lower  half  of  the  road,  it  should  be  distributed  to  a  uniform 
depth  by  the  use  of  a  blade  grader,  drag  scraper,  or  otherwise.  While 
this  course  is  being  spread,  all  the  larger  stone  should  be  raked  or  other- 
wise placed  directly  in  contact  with  the  subgrade.  Upon  this  course  of 
gravel  there  should  be  placed  such  an  amount  of  bonding  clay  as  may  be 
necessary  in  order  that  the  gravel  will  comply  with  the  specifications. 

After  the  gravel  has  been  spread  it  should  be  thoroughly  harrowed 
several  times  over  until  the  cores  formed  by  dumping  it  have  been  entire- 
ly loosened  up  to  a  density  equal  to  that  in  the  other  portions  of  the  gravel. 
The  importance  of  this  thorough  harrowing  can  scarcely  be  overestimated, 
for  in  order  to  secure  the  results  it  is  essential  that  the  voids  in  the  gravel 
be  reduced  to  a  minimum,  which  means  that  a  maximum  density  of  mate- 
rial must  be  obtained,  and  this  density  is  closely  approached  by  harrowing 
until  the  pebbles  of  the  several  sizes  become  so  placed  as  to  occupy  the 
spaces  between  those  of  a  large  size.  The  cost  of  this  harrowing  as  com- 
pared with  the  results  obtained  is  practically  negligible,  and  if  necessary 
it  would  actually  be  more  advisable  to  do  away  with  the  rolling  and  retain 
the  harrowing  than  to  do  away  with  the  harrowing  and  retain  the  rolling. 
The  harrow  should  be  of  the  stiff  tooth  type,  and  should  have  metal  teeth 
at  least  1-inch  in  diameter,  extending  about  6  inches  below  the  frame. 
The  spacing  of  the  teeth  should  be  such  as  will  admit  of  the  free  passage 
of  the  stones  between  them,  and  yet  so  displace  them  as  to  produce  the 
density  desired.  The  design  of  the  harrow  should  provide  a  weight  of 
from  8  to  12  pounds  upon  each  tooth. 

After  the  second  course  of  gravel  has  been  placed,  it  should  be  spread 
until  its  upper  surface  comes  flush  with  the  top  of  the  side  forms  and  its 
cross  section  conforms  to  that  desired.  The  forms  should  then  be  removed 
and  the  gravel  allowed  to  take  its  natural  position.  Upon  this  second 
course  there  should  be  distributed  the  necessary  quantity  of  bonding 
clay.  It  should  then  be  thoroughly  harrowed  several  times,  as  before, 
until  the  cores  formed  by  dumping  the  gravel  have  been  entirely  loosened 
up  and  the  clay  has  been  uniformly  distributed  throughout.  The  har- 
rowing should  continue  until  a  uniform  density  of  material  is  obtained 
throughout  the  upper  course. 

Having  done  this,  the  earth  shoulders  should  be  shaped  by  the  nec- 
essary cutting  and  filling  until  the  cross  section  conforms  approximately 
to  the  finished  work.  Material  other  than  the  natural  earth  should  not 
be  used  in  forming  these  shoulders,  and  all  vegetable  matter  should  be 
strictly  prohibited  from  entering  into  the  work.  Upon  having  shaped  the 
shoulders,  the  graded  roadway  over  the  entire  width  should  be  rolled  sev- 
eral times  over  until  it  is  thoroughly  compacted,  forming  a  firm,  smooth 
surface,  free  from  waves  and  according  to  the  requirement  of  the  plans. 
The  rolling  should  begin  at  the  extreme  outer  edges  of  the  shoulders  and 
should  work  toward  the  center,  at  each  rolling  of  the  gravel  allowing  an 
overlap  of  one-half  of  the  width  of  one  of  the  rear  wheels,  and  each  wheel 
should  cover  the  entire  gravel  surface. 

Should  the  condition  of  the  gravel  or  its  bonding  material  be  such  as 
not  to  compact  readily  under  the  action  of  the  roller,  sprinkling  or  other 
means  should  be  employed  to  compact  the  gravel  as  the  engineer  may 
direct.  The  speed  of  the  roller  should  not  exceed  about  100  feet  per  min- 
ute. It  is  quite  probable  that  after  rolling  there  will  appear  either  on 
the  shoulders  or  the  gravel  certain  depressions  and  other  irregularities. 
To  correct  these  defects  suitable  material  should  be  added  or  removed 
and  they  should  then  be  rerolled.  The  finished  surface  should  conform 
to  the  cross  section  shown  on  the  plan  and  should  present  a  smooth  and 


GRAVEL   ROADS  59 

even  appearance.  Should  the  gravel,  with  its  natural  or  artificial  mixture 
of  bonding  clay,  for  the  upper  4  inches  of  the  road,  be  of  such  character 
that  it  will  not  insure  a  satisfactory  wearing  surface  with  a  dense  body 
and  uniform  texture,  a  1-inch  coating  of  bonding  gravel  should  be  applied 
uniformly  over  the  entire  surface  of  the  gravel  road.  This  bonding  gravel 
should  then  be  raked  and  rolled  into  the  road  surface  until  all  the  inter- 
stices are  filled  and  the  surface  is  smooth,  of  a  uniform  texture  and  free 
from  waves. 

Screened  Gravel  Roads 

In  some  States,  preference  is  given  to  gravel  roads  built  like 
macadam  roads,  the  gravel  being  screened  so  that  the  courses 
will  be  composed  of  material  of  different  sizes.  This  is  the  case  in 
Wisconsin,  for  instance.  In  that  State,  except  on  sandy  road- 
beds, construction  is  started  at  the  end  of  the  road  farthest  from 
the  gravel  supply,  when  screened  gravel  is  used,  because  the 
roller  can  be  run  continuously  without  interfering  with  the  teams 
bringing  the  gravel.  The  first  course  consists  of  material  from 
If  to  about  3  inches  in  size  spread  to  a  loose  depth  of  6  inches. 
The  voids  are  filled  with  gravel  under  ^-inch  in  size  and  the  road 
is  then  rolled.  This  course  is  laid  for  a  distance  of  about  400 
feet,  and  the  second  course  is  then  started.  This  consists  of 
about  5  inches  of  $  to  IJ-inch  stone  with  the  voids  filled  like 
those  of  the  bottom  course.  The  surface  is  shaped  with  a  grader 
and  rolled  and  flushed  like  a  macadam  road. 

In  many  instances  better  results  are  obtained,  according  to 
J.  T.  Donaghey,  chief  inspector  of  the  Wisconsin  highway  com- 
mission, by  crushing  the  gravel  fine  enough  for  practically  all 
the  material  to  pass  a  If-inch  ring.  The  screen  is  partly  jack- 
eted so  that  just  enough  of  the  material  passing  the  §-inch  open- 
ings is  carried  into  the  }  to  If-inch  size  to  fill  the  voids  in  the 
latter.  This  mixture  is  used  in  both  the  bottom  and  top  courses 
and  results  in  a  type  of  road  which  Mr.  Donaghey  considers 
more  easily  built,  more  satisfactory  and  more  cheaply  maintained 
than  any  other  gravel  type.  Where  clay  is  added  to  assist  in 
binding  or  there  is  naturally  an  excessive  amount  of  clay  in  the 
gravel,  it  is  advisable  to  place  a  covering  of  sharp  sand  or  gravel 
on  the  finished  surface  to  protect  it  until  the  excess  clay  has  worked 
to  the  surface  and  washed  off. 

In  the  work  in  Kane  county,  Illinois,  to  which  reference  has 
already  been  made,  George  N.  Lamb,  county  superintendent  cf 
highways,  places  the  lower  course  in  a  trench  or  box  and  rolls  it 
and  the  shoulders  until  there  is  no  difference  of  elevation  where 
they  meet.  The  second  course  is  then  placed  with  the  edges 
feathering  out  a  foot  or  two  over  the  shoulders. 

The  following  instructions  for  preparing  the  subgrade  were 
issued  in  1914  by  the  Wisconsin  highway  commission: 


60  AMERICAN  HIGHWAY  ASSOCIATION 

Starting  at  the  desired  point,  set  two  stakes  opposite  the  reference 
stake,  the  distance  between  them  being  the  width  of  the  new  road.  To 
do  this,  refer  to  the  grade  sheet,  which  gives  the  distance  from  the  side 
stake  (placed  when  the  survey  was  made)  to  the  center  of  the  new  road. 
Subtract  from  this  distance  one-half  the  desired  width  of  road  and 
put  in  a  stake  with  inside  edge  at  this  distance  from  the  reference  stake. 
Opposite  this  stake  place  another  with  its  inside  edge  distant  the  width 
of  the  road  from  the  inside  edge  of  the  first  one.  All  stakes  forsubgrade 
should  be  made  of  £-inch  round  iron  about  24  inches  long,  and  about  twenty- 
five  should  be  kept  on  each  surfacing  job.  Stake  out  700  or  800  feet  at  a 
time.  Be  sure  that  the  stakes  are  in  line,  except  at  bends  or  on  curves. 
Usually  curves  will  have  to  be  staked  out  by  eye  to  get  good  results. 

With  a  road  plow  cut  as  close  to  the  inside  edge  of  stakes  as  possible 
withour  disturbing  them,  turning  the  furrow  toward  the  center  of  sub- 
grade.  Plow  about  5  inches  deep.  One  furrow  on  each  side  is  generally 
sufficient.  Plow  should  be  equipped  with  shoe  or  wheel  and  coulter.  If 
a  rooter  is  used,  three  furrows  on  each  side  will  usually  be  necessary.  Make 
first  cut  about  5  inches  deep  as  close  to  stakes  as  possible,  the  next  6  inches 
nearer  the  center  of  the  road.  Drop  the  shoe  down  so  rooter  will  run 
about  3  inches  deep  for  the  third  cut,  working  6  inches  nearer  center  of 
subgrade  than  previous  furrow. 

A  light  grader  that  can  be  handled  with  two  horses  is  best  for  shaping. 
Use  with  the  blade  so  set  as  to  move  the  plowed  ground  from  the  center 
of  trench  or  subgrade  on  to  the  bank  outside  of  stake  line.  This  work 
cannot  be  accomplished  neatly  with  the  grader  alone,  as  some  of  the  earth 
will  roll  back  into  the  trench  under  the  best  of  conditions.  Make  the 
trench  deep  enough.  The  depth  at  the  sides  should  be  at  least  the  total 
loose  depth  of  the  two  courses  of  material  and  more  than  this  on  sandy 
soils.  It  is  much  easier  to  throw  out  excess  material  with  the  road  grader 
after  the  surface  is  laid  than  it  is  to  bring  extra  material  up  from  the 
ditches  or  to  haul  it  in  by  wagons  during  the  finishing  when  the  trench  has 
not  been  made  deep  enough  to  hold  the  stone.  Nothing  is  more  essential 
than  a  good  solid  shoulder,  and  the  time  to  get  it  is  before  material  is 
placed  in  the  trench.  In  clay  soils  after  making  the  trench,  plow  drains 
through  the  shoulders  every  50  feet  on  both  sides  and  every  25  feet  at  low 
points  between  hills  and  immediately  clean  them  out  so  they  will  drain 
the  subgrade  in  case  of  rain. 

The  following  procedure  is  not  advised,  as  it  is  usually  the  most  expen- 
sive way  of  getting  shoulders.  If  the  road  has  once  been  covered  with 
crushed  stone  or  gravel,  and  it  is  not  desired  to  tear  up  the  old  surface, 
shoulders  can  be  brought  up  to  the  stakes  by  bringing  in  dirt  with  the 
road  machine  from  the  side  banks  or  from  the  ditches  (if  the  latter  mate- 
rial is  fit  to  use),  or  can  be  hauled  in  with  wagons.  If  the  old  road  has  a 
crown  of  one  inch  to  the  foot,  it  will  take  approximately  1,100  cubic  yards 
of  compacted  material  per  mile  to  build  up  6-inch  shoulders  and  retain  the 
minimum  width  of  20  feet  on  top.  The  cost  of  hauling  and  placing  this 
material  is  usually  very  much  greater  than  the  value  of  the  stone  or  gravel 
saved.  As  a  matter  of  fact,  no  material  is  wasted  if  the  subgrade  or  trench 
is  cut  in  the  old  surface,  the  stone  or  gravel  thrown  out  making  an  excel- 
lent shoulder.  Failure  is  inevitable  if  an  attempt  is  made  to  build  a  gravel 
or  stone  road  with  a  heavy  roller  without  first  getting  proper  shoulders 
to  support  the  material  while  it  is  being  rolled. 

Straighten  up  stakes  and  drive  them  firmly.  Tie  a  chalk  or  binder 
twine  line  to  stakes  on  each  side  so  line  will  draw  on  inside  faces  of  stakes, 
drawing  it  tight.  It  is  usually  best  to  put  in  additional  stakes  at  50-foot 
points  so  this  line  will  not  sag.  These  lines  a»e  to  guide  the  laborer  in 
trimming  the  shoulders  so  the  edges  will  be  straight  and  the  grade  uni- 


GRAVEL   ROADS 


61 


form.  On  a  9-foot  road,  if  these  lines  are  set  7  inches  above  center  of 
subgrade,  they  will  be  1  foot  higher  than  the  bottom  of  trench  at  the 
shoulder.  On  a  15-foot  road  set  lines  6  inches  above  center  of  subgrade. 
They  will  then  be  one  foot  higher  than  the  bottom  of  trench  at  the  shoulder. 
The  blade  of  an  ordinary  square  point  dirt  shovel  is  1  foot  long  and  can  be 
used  by  the  laborer  to  tell  when  trench  is  deep  enough  at  sides  by  setting 
blade  of  shovel  up  to  line.  When  trench  is  finished,  it  should  run  with  a 
uniform  slope  from  center  to  edge.  Clean  out  drainage  trenches  through 
shoulders,  so  that  they  really  drain  out  from  the  trench.  This  will  keep 
the  trench  from  filling  up  in  case  it  rains.  It  is  well  to  widen  the  trencn 
and  road  on  the  inside  of  curves,  and  to  elevate  the  outer  edge  of  curves. 
After  the  subgrade  has  been  properly  shaped  to  the  same  crown  (or, 
better,  a  slightly  greater  crown)  than  the  finished  road  is  to  have,  it  should 
be  rolled  until  hard,  especially  if  recently  filled.  Any  hollows  that  devel- 
op during  the  rolling  snould  be  filled.  Roll  enough,  but  stop  before  the 
top  layer  of  earth  starts  to  slip.  Wet  spots  in  the  subgrade  should  be 
shoveled  out,  filled  with  good  earth  or  cinders  and  rolled.  Don't  leave 
sink  holes  with  the  expectation  of  filling  them  with  crushed  stone.  They 
must  be  dug  out  and  refilled  with  good  material  if  a  firm  surface  is  to  ever 
be  gotten  at  that  point. 

In  spreading  gravel  or  broken  stone  many  engineers  place  on 
the  subgrade  wood  or  concrete  blocks  of  the  desired  loose  depth 
of  the  course.  In  Wisconsin,  however,  the  material  is  spread  by 
requiring  a  load  to  cover  a  certain  length  and  width  of  surface. 
The  foreman  is  given  a  table  of  the  length  of  9-foot  road  which 
loads  of  different  sizes  will  cover  and  the  spreader  is  required  to 

Length  of  Road  in  Linear  Feet  Which  a  Load  of  Stone  of  Given  Size  will 
Cover  to  the  Given  Loose  Depths.  Based  on  Table  of  Wisconsin  Highway 
Commission. 


WIDTH 

or   ROA.D 

LOOSE 
DEPTH 

SIZE   OF  LOAD  IN  CUBIC  YARDS 

1 

1} 

ij 

1! 

2 

2* 

2* 

2! 

8 

ftet 

inches 

feet 

feet 

feet 

feet 

feet 

feet 

feet 

feet 

feet 

8 

3 

13.5 

16.9 

20.2 

23.6 

27.0 

30.4 

33.7 

37.1 

40.5 

4 

10.1 

12.6 

15.2 

17.7 

20.2 

22.6 

25.3 

27.8 

30.3 

5 

8.1 

10.1 

12.1 

14.1 

16.2 

18.2 

20.2 

22.3 

24.3 

6 

6.75 

8.4 

10.1 

11.8 

13.5 

15.2 

16.9 

18.5 

20.3 

9 

3 

12 

15 

18 

21 

24 

27 

30 

33 

36 

4 

9 

11.25 

13.5 

15.75 

18 

20.25 

22.5 

24.75 

27 

5 

7.2 

9 

10.8 

12.6 

14.4 

16.2 

18 

19.8 

21.6. 

6 

6 

7.5 

9 

10.5 

12 

13.5 

15 

16.5 

18 

10 

3 

10.8 

13.5 

16.2 

18.9 

21.6 

24.3 

27 

29.7 

32.4 

4 

8.1 

10.1 

12.2 

14.2 

16.2 

18.2 

20.2 

22.3 

24.2 

5 

6.5 

8.1 

9.7 

11.3 

13.0 

14.6 

16.2 

17.8 

19.4 

6 

5.4 

6.7 

8.1 

9.4 

10.8 

12.1 

13.5 

14.8 

16.2 

12 

3 

9 

11.2 

13.5 

15.8 

18.0 

20.2 

22.5 

24.7 

27.0 

4 

6.7 

8.4 

10.1 

11.8 

13.5 

15.1 

16.9 

18.5 

20.2 

5 

5.4 

6.7 

8.1 

9.4 

10.6 

12.1 

13.5 

14.8 

16.2 

6 

4.5 

5.6 

6.7 

7.8 

9 

10.1 

11.2 

12.3 

13.5 

62  AMERICAN   HIGHWAY  ASSOCIATION 

make  the  loads  cover  just  this  length.  When  this  method  is 
followed  it  is  convenient  to  have  the  loads  hauled  of  the  same 
size.  The  man  placed  in  charge  of  the  spreading  should  be  se- 
lected carefully,  because  a  large  amount  of  money  can  be  wasted 
by  placing  too  much  material  on  the  road.  The  depth  of  the 
loose  material  should  be  checked  as  often  as  possible  on  this 
account. 

When  the  gravel  is  bought  by  weight  it  is  the  Wisconsin  rule 
to  take  the  weight  of  a  cubic  yard  of  pit  gravel  at  3000  pounds 
and  of  crushed  gravel  at  2650  pounds.  If  the  material  is  wet 
it  will  weigh  more  than  when  it  is  in  a  normal  condition  and  al- 
lowance should  be  made  for  this. 

Special  Binders 

Gravel  roads  are  now  being  built  for  quite  heavy  traffic  with 
binders  giving  greater  toughness  to  the  road  than  clay  or  rock 
powder  will  afford.  Examination  of  many  roads  after  several 
years  of  use  has  shown  that  there  is  less  large  stone  and  more 
small  stone  in  them  than  when  they  were  built.  This  change 
is  considered  due  to  the  internal  disintegration  of  the  stone  by 
the  loads  coming  upon  it,  part  of  the  reduction  taking  place  when 
the  road  is  heavily  rolled  during  construction  and  part  later  under 
heavy  travel.  The  special  binders  are  used  to  hold  the  stone  so 
firmly  together  that  after  the  rolling  of  the  road  there  will  be  no 
further  internal  disintegration.  The  method  of  using  bituminous 
binders  for  this  purpose  is  explained  in  the  chapter  on  bitumi- 
nous roads,  and  the  method  of  using  glutrin  in  the  chapter  on 
broken  stone  roads. 

Maintenance 

The  maintenance  of  gravel  roads  must  begin  immediately 
after  the  road  is  thrown  open  to  travel.  A  small  hole  in  a  gravel 
road,  unless  immediately  repaired,  soon  becomes  a  large  hole.  A 
few  large  holes  mean  a  ruined  road  and  a  large  expense  for  resur- 
facing. Furthermore  a  gravel  road,  no  matter  how  well  rolled, 
cannot  be  considered  finished  until  traffic  has  gone  over  it  and 
tested  every  part.  For  this  reason,  some  engineers  allow  traffic 
on  the  road  before  the  roller  has  left  it,  so  that  any  weak  places 
may  be  revealed  and  repaired  at  once  while  the  equipment  is 
still  at  hand.  The  rounded  pebbles  of  pit  gravel  do  not  inter- 
lock like  pieces  of  crushed  stone  but  are  usually  held  together 
by  a  clay  binder  which  is  not  so  strong  as  the  cementitious  pow- 
der from  some  classes  of  rock.  Until  travel  has  broken  down 
the  pebbles  and  furnished  rock  powder  which  will  act  with  the 
clay  and  form  a  rigid  mass,  a  gravel  road  is  not  so  firm  as  a  crushed 
stone  road  and  needs  more  maintenance. 


GRAVEL   ROADS  63 

The  gravel  roads  of  New  Hampshire  are  used  throughout  the 
summer  by  a  heavy  automobile  traffic,  particularly  on  Satur- 
days and  Sundays.  They  are  nevertheless  kept  in  good  condition 
by  the  patrol  system  of  maintenance  at  very  low  cost,  consider- 
ing the  destructive  use  to  which  they  are  subject.  Each  patrol- 
man has  a  section  for  which  he  is  responsible,  and  a  number  of 
sections  are  united  in  a  division  under  the  general  supervision 
of  a  maintenance  foreman,  who  is  in  immediate  charge  of  all  main- 
tenance work  and  reports  to  the  division  engineer.  Each  patrol- 
man must  supply  a  horse  and  dump  cart,  shovel,  pick,  hoe, 
rake,  stone-hook,  axe,  iron  bar,  iron  chain  and  tamp.  Special 
tools  are  furnished  by  the  State  highway  department.  The  meth- 
ods of  maintainance  are  indicated  in  the  following  quotations 
from  the  instructions  issued  to  the  patrolmen: 

One  dragging  in  the  spring  is  worth  two  in  the  summer.  It  is  better 
to  drag  a  mile  of  road  several  times  and  get  it  in  good  condition,  than  to 
drag  2  or  3  miles  and  not  finish  any  part  of  it.  Don't  drag  a  soft  section 
when  it  is  so  wet  that  the  first  vehicle  to  pass  will  rut  it  all  up.  First 
fill  the  holes  and  ruts  with  new  material  and  then  drag  as  the  surface  dries 
out.  Every  patrolman  should  have  material  dumped  in  small  piles  along 
the  side  of  his  section  so  that  on  a  rainy  day  he  can  at  once  fill  all  holes 
and  ruts  in  which  water  is  collecting. 

When  the  weather  is  unsuitable  for  dragging,  as  during  a  dry  spell,  all 
patrolmen  should  cart  on  all  the  new  material  possible  in  order  to  fill  all 
ruts  and  holes  and  resurface  worn-sections.  Carting  is  very  essential 
during  dry  periods  and  should  never  be  neglected.  Whenever  a  patrolman 
is  in  doubt  as  to  what  to  do  next  the  general  rule  is  to  cart  new  material, 
for  all  roads  are  wearing  out  under  travel  and  it  is  necessary  that  the 
surface  be  continually  renewed  to  take  the  place  of  the  old  material  that 
is  thrown  out  as  mud  or  blown  away  as  dust. 

Save  all  the  sods,  leaves,  rubbish,  stones  and  refuse  that  you  clean  off 
your  road  and  dump  this  waste  material  in  places  where  the  bank  is  steep 
so  that  by  flattening  the  side  slope  there  will  be  no  need  of  a  guard-rail, 
or  dump  the  material  back  of  a  present  guard-rail  so  that  later  this  guard- 
rail can  be  removed. 

Oiling  gravel  roads  generally  requires  careful  preparation  of 
the  surface  because  the  large  amount  of  clay  binder  has  a  ten- 
dency to  interfere  with  the  formation  of  a  satisfactory  oiled 
surface.  Consequently  the  surface  should  be  thoroughly  cleaned 
and  a  comparatively  light  oil  used.  The  first  applications  are 
likely  to  be  disappointing,  but  if  holes  and  ruts  are  filled  promptly, 
two  or  three  applications  on  carefully  cleaned  surfaces  during 
the  first  year  will  eventually  give  a  good  wearing  surface,  pro- 
vided the  roadbed  and  gravel  have  been  thoroughly  consolidated 
and  the  traffic  is  not  too  heavy  for  this  type  of  road.  It  is  the 
general  opinion  at  present  that  surface  applications  should  not 
be  made  until  a  gravel  road  has  had  at  least  one  year's  service. 
The  methods  of  doing  the  work  are  given  in  a  later  chapter. 


WATER-BOUND  MACADAM  ROADS 

Water-bound  macadam  roads  are  adapted  to  highways  carry- 
ing moderate  traffic,  for  experience  shows  that  even  when  a  large 
part  of  the  traffic  is  motor-driven  this  type  of  construction  can 
be  maintained  successfully  by  surface  applications,  as  described 
in  a  later  chapter.  Where  a  gravel  road  is  not  quite  able  to  carry 
the  traffic,  a  macadam  top  course  on  a  gravel  base  has  been 
adopted  as  a  standard  type  by  the  highway  departments  of  a 
number  of  States.  The  following  statements  give  the  views 
regarding  water-bound  macadam  held  by  three  State  highway 
departments  having  a  large  mileage  of  it  under  their  charge: 

New  York:  The  department  is  still  building  a  large  mileage  of  water- 
bound  macadam.  Because  of  the  presence  of  local  material  and  other  fa- 
vorable conditions  this  is,  in  cost,  the  cheapest  durable  road  which  can  be 
built;  and  it  is  the  belief  of  the  department  that  on  all  roads  of  ordinary 
or  light  traffic  this  type  is  still  a  satisfactory  one  for  general  use.  Of 
course  this  type  must  have  surface  treatment  with  oil,  and  this  is  planned 
for  in  all  cases.  (Edwin  Duffey,  State  commissioner  of  highways,  1916. ) 
Michigan:  During  the  early  existence  of  the  department,  macadam 
roads  constituted  as  much  as  50  per  cent  of  the  mileage  constructed.  As 
the  use  of  the  automobile  became  more  widespread,  the  percentage  of 
macadam  roads  built  each  year  decreased,  owing  to  the  excessive  cost  of 
maintaining  this  type  under  the  automobile  traffic.  Within  the  past  two 
years,  however,  waterbound  macadam  roads  have  been  again  growing  in 
favor,  because  it  has  been  found  possible  with  a  bituminous  surface  treat- 
ment to  maintain  them  in  a  condition  comparable  in  the  point  of  service 
to  the  higher  types  of  roads.  The  first  treatment,  which  is  made  after 
the  road  has  been  seasoned  by  opening  it  to  traffic  for  three  or  four  months, 
is  essentially  a  part  of  the  initial  cost  of  construction.  (Frank  F.  Rogers, 
State  highway  commissioner,  1916.) 

Wisconsin:  It  is  not  at  all  an  economical  type  of  surfacing  unless  in- 
tensely maintained  with  surface  treatments  and  a  patrol  system,  but  when 
so  maintained  gives  economical  service  even  on  heavily  traveled  roads. 
(Wisconsin  highway  commission,  1916.) 

Stone 

The  roadbuilding  properties  of  different  rocks  are  explained  in 
the  next  chapter.  The  following  notes  on  the  selection  of  stone 
were  prepared  by  Prevost  Hubbard  and  Frank  H.  Jackson,  Jr.1 
The  ideal  rock  for  the  construction  of  a  water-bound  macadam 

1  "The  Results  of  Physical  Tests  of  Road-building  Rock,"  Bulletin  370, 
United  States  Department  of  Agriculture. 

64 


WATER-BOUND  MACADAM  ROADS 


65 


road  resists  the  wear  of  traffic  to  which  it  is  subjected  to  just 
that  extent  which  will  supply  a  sufficient  amount  of  cementitious 
rock  dust  to  bind  or  hold  the  larger  fragments  in  place.  It  is 
generally  admitted  that  the  ordinary  macadam  road  is  not  well 
suited  to  any  considerable  amount  of  automobile  traffic,  because 
such  traffic  rapidly  removes  the  binder  without  producing  fresh 
material  to  take  its  place. 

Cementing  value  is  a  necessary  quality  for  rocks  used  in  mac- 
adam road  construction.  As  determined  by  test,  cementing 
values  below  25  are  called  low;  from  26  to  75,  average,  and  above 
75,  high.  In  general,  the  cementing  value  should  run  above  25. 
For  rocks  which  show  a  low  French  coefficient  of  wear,  however, 
a  relatively  high  cementing  value  is  more  necessary  than  for 
those  which  have  a  high  French  coefficient.  Interpretation  of 
results  of  the  cementing  value  test  is  subject  to  a  number  of 
influencing  considerations.  For  instance,  it  has  been  found  that 
certain  feldspathic  varieties  of  sandstone  give  excellent  results 
in  this  test,  while  experience  has  shown  that  they  do  not  bind 
well  when  used  in  the  wearing  course  of  macadam  roads.  In 
the  case  also  of  certain  varieties  of  the  trap  group,  low  results 
are  frequently  shown  by  laboratory  tests  for  rocks  which  bind 
quite  satisfactorily  upon  the  road,  provided  traffic  is  sufficiently 
heavy  to  supply  the  requisite  amount  of  fine  material.  Certain 
granites,  gneisses,  and  schists  which  are  not  suitable  for  use  as 
binding  material  give  good  results  in  this  test.  In  such  cases 
it  is  usually  found  that  the  highly  altered  nature  of  the  material 
reduces  its  toughness  and  resistance  to  wear  to  such  an  extent 
as  to  condemn  it  for  use. 

Experience  has  shown  that  in  general  the  following  table  of 
limiting  values  for  the  French  coefficient  of  wear,  toughness,  and 
hardness  may  be  used  in  determining  the  suitability  of  a  rock 
for  the  construction  of  the  wearing  course  of  a  macadam  road: 

Limiting  Values  of  Physical  Tests  of  Rock  Suitable  for  Water-bound 

Macadam 


TRAVEL 

FRENCH 
COEFFICIENT 

PERCENTAGE 
OF   WEAR 

TOUGHNESS 

HARDNESS 

Light  

5  to    8 

5      to  8 

5  to    9 

10  to  17 

Moderate  

9  to  15 

2  7  to  5 

10  to  18 

14  or  over 

Heavy 

16  or  over 

Under  2  7 

19  or  over 

With  relation  to  the  limitations  for  hardness  it  may  be  noted 
that  when  any  given  value  for  toughness  falls  within  certain 
limits  which  define  the  suitability  of  the  material  for  macadam 
road  construction  under  given  traffic  conditions,  the 


corre- 


66  AMERICAN  HIGHWAY  ASSOCIATION 

spending  value  for  hardness  will  fall  within  similar  limits  for  hard- 
ness. In  this  connection  it  will  be  seen  in  the  table  that  a  max- 
imum limit  for  hardness  is  only  given  in  the  case  of  light  traffic. 
It  has  been  found  that  the  great  majority  of  samples  having  a 
French  coefficient  of  wear  of  from  5  to  8  and  a  hardness  of  over 
17  are  granites,  quartzites,  and  hard  sandstones,  which  are  unsuited 
for  use  in  the  wearing  course  of  water-bound  macadam  roads 
due  to  their  lack  of  binding  power. 

The  weight  of  a  cubic  yard  of  crushed  stone  varies  consider- 
ably, depending  upon  the  rock,  the  size  to  which  it  is  broken 
and  the  amount  of  shaking  the  sample  receives  before  its  volume 
is  measured.  The  range  in  weight  of  a  cubic  foot  of  solid  rock 
is  162  to  221  pounds  for  trap,  165  to  200  pounds  for  schist,  156 
to  175  pounds  for  felsite,  156  to  193  pounds  for  quartzite,  125 
to  193  pounds  for  limestone,  and  125  to  187  pounds  for  granite. 
The  total  range  from  the  lightest  limestone  to  the  heaviest  trap 
is  over  75  per  cent  and  the  crushed  rock  will  show  the  same  varia- 
tions. Consequently,  when  broken  stone  is  bought  by  weight 
it  should  be  actually  weighed  before  estimating  the  quantity  re- 
quired for  good  work. 

Crushed  stone  is  the  most  important  branch  of  the  stone  in- 
dustry. The  production  of  this  material  for  road  building  in 
the  different  states  is  given  in  a  table  on  page  198  of  this  book. 
The  requirements  for  railroad  ballast  and  concrete  as  well  as  for 
road  work  are  so  large  that  commercial  broken  stone  is  avail- 
able in  many  parts  of  the  country  at  a  lower  price  than  the  cost 
of  quarrying  and  crushing  local  material.  It  is  sometimes  eco- 
nomical, even  at  a  greater  initial  cost,  to  import  stone  from  a 
distance  if  thereby  a  more  durable  road  may  be  had  than  is  pos- 
sible with  the  use  of  local  stone. 

Much  of  the  stone  is  crushed  locally,  usually  in  portable  plants. 
These  comprise  a  crusher  with  an  engine  and  boiler,  revolving 
screens,  portable  bins  and  an  elevator  to  lift  the  stone  after  it 
is  crushed  into  the  screen  and  sometimes  into  the  bins.  The 
capacity  of  a  crusher  should  be  adjusted  to  the  road  roller  ca- 
pacity. If  the  crusher  furnishes  more  stone  than  the  roller  can 
consolidate,  it  is  too  large  to  work  economically.  If  the  crusher 
can  not  supply  enough  stone  to  keep  the  roller  at  work,  the  lat- 
ter will  operate  uneconomically.  Furthermore  the  arrangements 
for  supplying  stone  from  the  crusher  to  the  road  must  be  such 
that  the  expensive  equipment  at  each  end  of  the  line  will  be 
kept  operating  all  the  time.  There  is  some  difference  of  opin- 
ion as  to  the  proper  capacity  of  a  crusher,  for  in  some  sections 
of  the  country  it  is  held  that  from  60  to  80  cubic  yards  of 
broken  stone  is  as  much  as  a  single  roller  will  consolidate  properly, 
while  in  other  sections  it  is  held  that  a  roller  which  does  not  con- 
solidate 75  tons  per  day  is  not  doing  good  service. 


WATER-BOUND   MACADAM  ROADS  67 

Where  the  stone  supply  is  limited  to  ledges  at  infrequent  inter- 
vals but  little  choice  in  the  location  of  the  crushing  outfit  is  pos- 
sible. If  field  stone  or  ledges  are  available  alongside  the  road 
at  frequent  intervals  a  crusher  can  serve  about  two  miles  of 
road  most  economically.  Local  conditions,  however,  affect  the 
proper  arrangement  of  the  plant  so  greatly  that  no  precise  rules 
can  be  drawn  up.  It  occasionally  happens  that  the  availability 
of  water  for  the  boiler  is  of  more  importance  than  any  other 
factor  in  determining  the  location  of  the  outfit. 

If  possible,  the  crusher  should  be  set  low  enough  so  that  a  plat- 
form can  be  built  at  the  level  of  the  opening  into  which  the  stone 
is  dumped.  The  carts  are  driven  onto  this  platform  and  the  ma- 
terial is  handled  most  economically  in  this  manner.  The  men  who 
set  up  the  plant  should  have  had  experience  in  this  work.  Much 
depends  on  the  proper  alignment  of  the  several  parts  and  the 
delays  in  operation  will  be  avoided  if  the  work  is  done  properly 
in  the  first  instance. 

The  screens  in  such  portable  plants  have  three  sections  about 
4  feet  long  and  30  inches  in  diameter.  The  first  section  has  per- 
forations which  are  ^-inch  in  diameter.  The  perforations  of  the 
second  section  are  generally  If  inches  in  diameter  where  com- 
paratively hard  stone  is  used  and  1%  inches  in  diameter  where 
softer  stone  is  employed.  With  the  very  soft  stone  used  in  some 
of  the  Central  States,  the  perforations  are  sometimes  2£  inches, 
and  the  third  section  of  the  screen  is  omitted.  The  perforations 
in  the  third  section  are  from  2  to  2$  inches  in  diameter  as  a  rule, 
depending  upon  the  maximum  size  of  the  stone  which  is  allowed 
in  the  road,  but  this  maximum  size  varies  widely  in  different 
States.  In  New  York  stone  up  to  3|  inches  in  size  is  used  in  the 
bottom  course  and  in  Ohio  pieces  of  sandstone  as  large  as  6  inches 
in  their  longest  dimensions  are  permitted  in  the  bottom  course 
of  some  roads.  Stone  passing  a  4-inch  circular  opening  is  also 
permitted  under  some  conditions.  In  Wisconsin  the  bottom 
course  is  usually  made  of  stone  2  to  3J  inches  in  size;  in  this  case 
the  perforations  in  the  screen  are  £,  2  and  3^  inches. 

The  stones  too  large  to  pass  through  the  openings  in  the  third 
section  of  the  screen  drop  out  and  are  run  through  the  crusher 
again.  There  is  sometimes  a  conveyor  to  carry  these  tailings 
from  the  end  of  the  screen  to  the  crusher.  The  jaws  of  the  crusher 
should  be  set  to  give  as  few  tailings  as  possible  and  the  length 
of  the  screen  sections  should  be  adjusted  to  accomplish  the  same 
purpose.  The  operation  of  the  screens  should  be  observed  from 
time  to  time  in  order  to  make  sure  that  material  which  should 
pass  the  openings  in  each  section  does  not  flow  along  the  screen 
so  rapidly  that  there  is  a  failure  to  separate  it  out  by  the  right 
section  of  the  screen.  If  the  screen  revolves  too  rapidly  fine 


68  AMERICAN  HIGHWAY   ASSOCIATION 

material  will  be  carried  into  the  coarser  grades.  Stone  purchased 
from  commercial  crusher  plants  is  often  observed  to  run  small, 
the  best  separation  occurring  in  the  product  which  is  obtained 
during  a  time  of  minimum  demand.  This  is  because  more  time 
is  then  given  to  the  stone  in  its  passage  through  the  screens. 
It  is  impracticable  to  obtain  a  complete  gradation  of  the  sizes 
of  stone  and  for  this  reason  highway  engineers  often  permit  vari- 
ations from  the  nominal  maximum  and  minimum  dimensions 
of  any  size.  For  instance  the  f-inch  stone  specified  in  New 
Jersey  may  contain  up  to  5  per  cent  of  material  larger  than  1 J  inch 
and  up  to  8  per  cent  smaller  than  f  inch,  although  the  nom- 
inal range  of  size  is  from  f  to  1J  inch. 

There  is  no  uniformity  in  the  designation  of  the  sizes  of  crushed 
stone;  what  is  termed  as  No.  1  stone  in  Ohio  is  entirely  different 
from  No.  1  stone  in  New  York. 

Drainage 

The  investment  in  a  macadam  road  is  so  great  that  every  pre- 
caution should  be  taken  to  have  the  roadbed  thoroughly  drained. 
The  methods  of  doing  this  were  explained  in  the  chapter  on 
drainage.  If  they  are  not  employed  wherever  necessary  the  road 
will  inevitably  become  rutted  and  marked  by  holes  during  pro- 
longed wet  weather,  and  the  maintenance  of  such  places  will 
entail  an  annual  expenditure  far  greater  in  the  end  than  the  cost 
of  proper  drainage  work. 

Formerly  Telford  foundations  were  used  in  all  wet,  soggy 
ground  under  well-built  broken  stone  roads  but  experience  has 
shown  that  with  good  underdrainage  equally  satisfactory  foun- 
dations can  be  built  of  coarse  gravel.  This  is  dumped  on  the 
bottom  of  the  road  after  the  soft  material  has  been  excavated 
to  a  considerable  depth.  The  mass  of  gravel  should  be  drained 
into  the  side  ditches  by  constructing  blind  drains  through  the 
shoulders  at  intervals  of  not  over  50  feet. 

Where  suitable  field  stone  is  available  for  a  Telford  foundation 
it  is  still  sometimes  used.  The  New  York  requirements  for 
stone  for  this  purpose  are  a  thickness  of  not  less  than  l£  inches, 
a  depth  equal  to  the  depth  required  for  the  foundation,  from  6 
to  8  inches,  and  a  length  not  more  than  one  and  a  half  times 
the  depth.  The  New  Jersey  specifications  require  stone  5  to 
10  inches  long,  2  to  4  inches  wide  and  at  least  6  inches  deep. 
Some  engineers  advise  placing  this  stone  on  a  bed  of  gravel,  while 
others  believe  that  if  gravel  is  available  it  is  best  to  make  the 
entire  base  of  it  and  not  employ  Telford,  since  the  latter  is  quite 
expensive.  The  stone  must  be  set  on  their  broader  base,  length- 
wise across  the  road,  and  wedged  by  driving  small  stone  into 


WATER-BOUND   MACADAM   ROADS  69 

the  interstices.  The  projecting  points  should  be  broken  off 
with  a  stone  hammer,  the  depressions  in  the  top  filled  with  stone 
chips,  and  the  foundation  rolled. 

The  V-shaped  drain  described  on  page  27  is  a  substitute  for 
a  Telford  foundation  which  has  received  much  favor  in  some 
states. 

Sub-Grade 

It  is  necessary  to  place  the  stone  for  a  macadam  road  in  a  box 
or  trench  in  order  to  roll  it  successfully.  The  method  of  exca- 
vating the  sub-grade  was  described  on  page  60.  The  bot- 
tom must  be  slightly  crowned.  This  is  for  two  reasons;  first  to 
shed  any  water  which  may  sink  through  the  macadam,  and 
second,  to  keep  the  amount  of  stone  required  for  the  road  to  the 
minimum  actually  necessary.  The  sub-grade  must  be  rolled 
until  hard  in  order,  first,  that  the  stone  placed  on  it  can  not  be 
driven  into  it  and  thus  serve  no  useful  purpose,  and  second,  to 
turn  toward  the  sides  of  the  road,  into  the  blind  drains  leading 
to  the  ditches,  any  water  which  may  penetrate  the  courses  of 
stone. 

The  depth  of  the  box  or  trench  is  fixed  by  the  desired 
depth  of  the  macadam  roadway.  This  is  rarely  less  than  6 
inches  at  the  center  and  is  sometimes  considerably  more,  al- 
though there  is  a  question  whether  a  greater  thickness  than  8 
inches  after  rolling  serves  any  useful  purpose.  The  harder  and 
tougher  the  stone,  the  less  need  be  the  thickness  of  the  road, 
provided  the  sub-grade  is  firm.  Usually  the  sides  of  the  macadam 
roadway  are  1  to  2  inches  thinner  than  the  center. 

On  very  sandy  soils,  to  keep  the  sand  from  working  up  through 
the  stone,  a  covering  of  clay,  hay,  straw,  or  fine  brush  is  spread 
over  the  subgrade. 

Placing  the  Broken  Stone 

It  is  customary  to  begin  placing  the  broken  stone  as  soon  as 
a  few  hundred  feet  of  the  subgrade  has  been  prepared  to  receive 
it,  because  it  is  undesirable  to  expose  the  rolled  earth  surface  to 
the  danger  of  drenching  by  rains  for  a  longer  period  than  is 
necessary. 

The  first  course  is  rarely  if  ever  spread  to  a  greater  depth  than 
6  inches  when  loose,  because  a  roller  cannot  compact  a  deeper 
course  of  stone  in  a  satisfactory  manner.  The  thickness  is  sel- 
dom less  than  4  inches.  The  largest  size  of  the  screened  stone 
is  used.  In  some  states  it  is  forbidden  to  dump  the  stone  di- 
rectly on  the  subgrade,  on  the  ground  that  this  leaves  a  mass  of 
consolidated  small  stone  in  the  center  of  the  heap  which  remains 


70 


AMERICAN  HIGHWAY  ASSOCIATION 


almost  intact  when  the  pile  is  leveled.  Accordingly  the  stone 
must  be  deposited  on  dumping  boards  about  6  feet  long  and  3 
feet  wide,  from  which  it  is  shoveled  to  the  subgrade.  This  is  no 
longer  a  generally  adopted  requirement,  however,  but  it  is  not 
unusual  to  require  a  load  to  be  deposited  in  several  dumps 
so  that  the  least  amount  of  shoveling  and  raking  will  be  required. 

Costs  Per  Mile  Corresponding  to  Different  Costs  Per  Square  Yard.    Based  on 
Table  Published  by  Commissioner  of  Public  Roads  of  New  Jersey 


Width,  feet 

Square 
yards, 
per  mile 

8 
4,693* 

10 

5.866J 

12 
7,040 

14 
8,213* 

16 
9,386} 

18 
10,560 

20 
11.7331 

Cost  per  sq. 

yd. 

$0.25 

$1,173.33 

$1,466.67 

$1,760.00 

$2,053.33 

$2,346.67 

$2,640.00 

$2,933.33 

0.30 

1,408.00 

1,760.00 

2,112.00 

2,464.00 

2,816.00 

3,168.00 

3,520.00 

0.35 

1,642.67 

2,053.33 

2,464.00 

2,874.67 

3,285.33 

3,696.00 

4,106.67 

0.40 

1,877.33 

2,346.67 

2,816.00 

3,285.33 

3,754.67 

4,224.00 

4,693.33 

0.45 

2,112.00 

2,640.00 

3,168.00 

3,696.00 

4,224.00 

4,752.00 

5,280.00 

0.50 

2,346.67 

2,933.33 

3,520.00 

4,106.67 

4,693.33 

5,280.00 

5,866.67 

0.55 

2,581.33 

3,226.67 

3,872.00 

4,517.33 

5,162.67 

5,808.00 

6,453.33 

0.60 

2,816.00 

3,520.00 

4,224.00 

4,928.00 

5,632.00 

6,336.00 

7,040.00 

0.65 

3,050.67 

3,813.33 

4,576.00 

5,338.64 

6,101.33 

6,864.00 

7,626.67 

0.70 

3,285.33 

4,106.67 

4,928.00 

5,749.33 

6,570.67 

7,392.00 

8,213.33 

0.75 

3,520.00 

4,400.00 

5,280.00 

6,160.00 

7,040.00 

7,920.00 

8,800.00 

0.80 

3,754.67 

4,693.33 

5,632.00 

6,570.67 

7,509.33 

8,448.00 

9,386.67 

0.85 

3,989.33 

4,986.69 

5,984.00 

6,981.33 

7,978.67 

8,976.00 

9,973.33 

0.90 

4,224.00 

5,280.00 

6,336.00 

7,392.00 

8,448.00 

9,504.00 

10,560.00 

0.95 

4,458.67 

5,573.33 

6,688.00 

7,802.67 

8,917.33 

10,032.00 

11,146.67 

1.00 

4,693.33 

5,866.67 

7,040.00 

8,213.33 

9,386.67 

10,560.00 

11,733.33 

1.05 

4,928.00 

6,160.00 

7,392.00 

8,624.00 

9,856.00 

11,088.00 

12,320.00 

1.10 

5,162.67 

6,453.33 

7,744.00 

9,034.67 

10,325.33 

11,616.00 

12,906.67 

1.15 

5,397.33 

6,746.67 

8,096.00 

9,445.33 

10,794.67 

12,144.00 

13,493.33 

1.20 

5,632.00 

7,040.00 

8,448.00 

9,856.00 

11,264.00 

12,672.00 

14,080.00 

NOTE:  When  the  cost  per  square  yard  is  greater  than  $1.20,  the  corre- 
sponding cost  per  mile  can  be  found  by  adding  to  the  tabulated  cost  for  a  rate 
of  $1.00  per  square  yard,  the  tabulated  cost  for  a  rate  equal  to  the  difference 
between  the  given  rate  and  $1.00.  The  costs  per  square  mile  for  widths 
greater  than  20  feet  are  found  by  adding  together  the  costs  for  two  of  the 
tabulated  widths  which  will  give  the  desired  width. 

The  easiest  method  of  distributing  the  stone  is  by  using  an  auto- 
matic spreader  wagon  which  deposits  it  in  a  layer  of  approxi- 
mately the  right  thickness.  The  methods  of  determining  the 
thickness  are  explained  on  page  61. 

When  a  hundred  feet  or  so  of  the  first  course  has  been  spread, 
the  rolling  should  begin.    A  roller  weighing  about  600  pounds 


WATER-BOUND   MACADAM   ROADS  71 

per  inch  of  width  of  roll  is  usually  recommended  for  rolling  hard 
rock,  but  one  of  three-fourths  this  weight  will  probably  do  bet- 
ter work  with  soft  limestone.  The  roller  starts  at  the  edges  of 
the  stone  and  care  should  be  taken  that  the  shoulders  are  not 
crushed  during  the  trips  near  the  sides  of  the  trench.  The  roller 
should  not  be  run  much  faster  than  100  feet  per  minute.  After 
both  sides  are  moderately  firm,  the  roller  should  move  gradually 
toward  the  center  until  the  whole  lower  course  is  thoroughly 
compacted.  The  rolling  should  be  stopped  as  soon  as  the 
pieces  of  stone  begin  to  break.  Sometimes  it  is  found  that 
a  wavy  motion  continues  and  the  stone  will  not  compact. 
This  may  be  due  to  a  wet  subgrade,  which  will  probably  give 
no  trouble  if  allowed  to  dry  for  a  day  or  two,  or  it  may  be  due 
to  the  use  of  a  very  hard  stone,  when  the  application  of  a  little 
sand  or  fine  gravel  may  remedy  the  difficulty.  With  some 
soft,  coarse,  gravel  stones  a  crawling  motion  may  be  noticed, 
which  can  be  prevented  by  a  light  sprinkling  of  coarse  sand, 
stone  screenings  and  sometimes  by  water.  The  rolling  is  con- 
tinued until  the  stone  has  no  movement  when  the  men  walk  over 
it.  If  depressions  develop  during  the  rolling  they  must  be 
filled  with  stone  of  the  same  size  as  that  used  in  the  course 
and  rolled  until  firm. 

Some  engineers  advise  harrowing  the  loose  stone  with  a  spike- 
tooth  harrow  in  order  to  mix  the  stone  thoroughly  and  to  save 
a  part  of  the  rolling.  This  would  be  of  advantage  if  full  loads  of 
stone  were  dumped  directly  on  the  subgrade,  for  it  would  break 
up  the  cores  of  small  stone  in  the  center  of  the  piles.  Other 
engineers  recommend  using  a  blade  grader  to  shape  the  loose 
stone  just  before  rolling. 

It  is  not  customary  to  apply  a  binder  of  gravel  or  screenings 
to  the  bottom  course  in  some  states  and  it  is  required  in  others. 
It  is  apparently  a  detail  depending  considerably  upon  the  hard- 
ness of  the  stone  used.  If  the  stone  is  relatively  soft  and  the 
bottom  course  is  constructed  of  a  large  size  of  stone,  a  binder 
may  prevent  the  internal  disintegration  of  the  stone  under  loads 
to  some  extent,  but  with  the  somewhat  smaller,  hard  trap  rock 
used  in  Massachusetts,  for  instance,  screenings  are  unnecessary. 

After  about  a  hundred  feet  of  the  bottom  course  has  been 
rolled,  the  second  course  is  spread.  This  consists  of  the  size  from 
J  to  li  or  1|  inches,  and  the  loose  depth  is  3  to  5  inches.  Large 
loads  should  not  be  dumped  directly  on  the  bottom  course.  The 
top  course  is  usually  given  its  final  shaping  with  rakes.  This 
course  is  rolled  commencing  on  each  outer  edge  with  the  rear 
wheel  half  on  the  stone  and  half  on  the  shoulders;  the  roller  is 
gradually  worked  toward  the  center.  If  depressions  are  devel- 
oped during  this  work,  they  must  be  filled,  and  the  rolling  should 
continue  until  the  surface  is  hard  and  uniform  in  contour. 


72  AMERICAN  HIGHWAY  ASSOCIATION 

The  surface  is  then  covered  with  the  binder.  The  material 
used  for  this  purpose  varies  with  the  character  of  the  stone  in 
the  top  course.  Generally  screenings  are  employed,  but  in  states 
where  the  top  course  is  composed  of  rather  large  sizes  of  stone 
the  screenings  have  small  stone  mixed  with  them.  In  Mary- 
land limestone  screenings  are  not  permitted  with  trap  rock  with- 
out the  consent  of  the  engineer.  A.  R.  Hirst,  State  highway  engi- 
neer of  Wisconsin,  advises  using  a  clayey  pea  gravel  or  disinte- 
grated granite  with  crushed  quartzite  or  granite,  and  if  these 
are  unavailable  he  prefers  a  bituminous  binder. 

Screenings  are  rarely  if  ever  permitted  to  be  dumped  on  the 
road.  They  should  be  placed  in  piles  along  the  road  at  such 
intervals  that  they  can  be  distributed  readily  and  enough  mate- 
rial will  always  be  available.  In  Massachusetts  it  is  not  cus- 
tomary to  place  the  screenings  to  a  greater  depth  than  1  inch. 
In  Michigan  the  depth  is  about  }  inch  and  in  Wisconsin  about 
J  inch  on  State  roads. 

Although  the  screenings  are  sometimes  rolled  dry,  after  being 
spread,  the  usual  practice  is  to  sprinkle  the  road  with  water 
before  rolling.  The  road  must  be  sprinkled  until  the  screenings 
are  thoroughly  wet  and  do  not  stick  to  the  wheels  of  the  roller. 
Where  hard,  small  stone  is  used  in  the  top  course  more  water 
is  generally  employed  than  where  the  stone  is  larger,  and  an 
attempt  is  made  to  flush  the  screenings  into  the  interstices  be- 
tween the  stones.  If  the  screenings  are  picked  up  by  the  roller 
at  any  time,  more  water  must  be  applied.  The  sprinkling  and 
rolling  are  continued  until  water  is  carried  along  in  front  of  the 
roller  wheels  at  every  point  of  the  road. 

Rolling  must  be  done  carefully  for  the  appearance  of  the  road 
will  depend  upon  this  work. 

After  the  road  has  dried  sufficiently,  the  shoulders  should 
be  smoothed  off  with  a  road  machine,  if  one  is  available.  The 
shoulders  should  be  trimmed  so  the  water  can  flow  from  the 
center  of  the  road  to  the  ditches  along  every  foot  of  the  way. 
All  surplus  material  should  be  removed,  and  the  shoulders  should 
be  rolled  as  far  out  as  it  is  safe  to  run  the  roller. 

Glutrin  Binder 

For  a  number  of  years,  glutrin  has  been  used  extensively  as 
a  binding  material  for  both  gravel  and  broken  stone  roads.  It 
is  an  adhesive  binding  liquid  whose  base  is  the  lignin  derived 
from  the  sulphite  pulp  wood  process.  It  is  sold  in  a  concentrated 
state  and  should  be  diluted  with  water  before  use. 

It  should  be  understood  that  when  the  road  material  to  be 
treated  is  other  than  stone,  it  should  contain  at  least  10  per  cent 


WATER-BOUND   MACADAM   ROADS  73 

of  clay.  When  this  is  lacking  in  the  original  road  material,  it 
should  be  evenly  added  as  the  road  material  is  put  in  place. 
When  used  on  gravel  or  sand-clay  roads,  glutrin  should  be  di- 
luted with  water  in  the  proportion  of  one  part  glutrin  to  not 
less  than  three  parts  water.  This  mixture  should  be  applied 
by  means  of  any  distributor  which  will  spread  it  uniformly. 
The  application  should  be  continuous,  so  that  the  road  is  kept 
moist,  but  not  so  rapidly  as  to  permit  the  forming  of  pools  or 
the  flowing  off  to  the  sides.  Penetration  must  be  secured,  and 
consequently  the  distributor  should  make  at  least  four  trips 
over  the  road  in  applying  the  amount  of  glutrin  called  for  in  the 
specifications.  This  is  usually  about  |  gallon  of  glutrin  to  the 
square  yard. 

When  used  in  the  construction  of  broken  stone  or  slag  roads, 
the  glutrin  should  be  applied  during  the  process  of  puddling 
the  top  course.  The  puddle  should  be  begun  as  usual  with  plain 
water,  but  as  soon  as  the  screenings  are  thoroughly  saturated, 
glutrin  should  be  placed  in  the  sprinkler  in  the  proportion  of  one 
part  glutrin  to  five  parts  water,  and  the  puddling  completed 
with  this  mixture.  The  specifications  usually  call  for  |  gallon 
of  glutrin  to  the  square  yard  to  be  used  in  this  process.  A  still 
stronger  bond  can  be  secured  if,  after  the  road  has  been  pud- 
dled in  this  manner,  it  is  allowed  to  dry  out  and  a  surface  ap- 
plication is  then  made  over  the  center  80  per  cent  of  the  width 
of  the  road,  of  0.2  gallon  of  glutrin,  diluted  in  the  proportion  of 
one  part  glutrin  to  three  parts  water.  As  soon  as  the  road  is 
dry,  it  can  be  opened  to  traffic. 

There  have  been  many  miles  of  glutrin-bound  roads  con- 
structed in  Connecticut  and  New  York,  which  have  been  given 
a  bituminous  top  course,  or  even  an  oil  treatment,  the  purpose 
being  to  bind  the  mass  of  stones  thoroughly  together  with  glu- 
trin to  prevent  the  internal  disintegration  of  the  gravel  or  stone 
by  traffic  and  to  protect  the  glutrin  from  surface  water. 

Glutrin  should  not  be  used  with  a  pure  siliceous  material  like 
quartz,  unless  at  least  10  per  cent  of  clay  is  added.  With  broken 
stone,  the  fine  material  produced  in  rolling,  furnishes  a  substi- 
tute for  the  clay  required  with  gravel. 

Maintenance 

Where  there  is  very  little  automobile  traffic  the  old-fashioned 
methods  of  maintenance  are  still  applicable.  If  the  road  was 
built  late  in  the  fall,  particularly  if  trap  rock  was  used,  it  is  pos- 
sible that  loose  stone  will  appear  on  the  surface  in  the  spring. 
They  should  be  removed  and  need  cause  no  apprehension.  Holes 
and  ruts  should  be  filled  with  small  stone  and  screenings,  prefer- 


74  AMERICAN   HIGHWAY   ASSOCIATION 

ably  during  a  rain  so  the  traffic  will  begin  to  bind  the  patch  as 
soon  as  the  weather  clears.  When  the  top  course  has  been  worn 
down  so  that  the  large  stone  of  the  bottom  course  show  in  places, 
the  road  should  be  repaired.  If  the  top  course  is  to  be  less  than 
3  inches  thick  the  stone  can  be  spread  on  the  road  and  treated 
like  the  top  course  of  a  new  road.  If  the  course  is  to  be  made 
of  3  inches  or  more  of  loose  stone,  it  is  generally  best  to  loosen 
up  the  road  by  means  of  spikes  placed  in  the  wheels  of  the  roller 
or  by  the  use  of  a  scarifier. 

This  method  of  maintenance  is  practically  obsolete  on  account 
of  motor  traffic.  The  shearing  action  of  the  wheels  of  an  auto- 
mobile on  a  water-bound  road  speedily  loosens  the  stones  of  the 
top  course  and  it  is  necessary  to  protect  the  surface  by  a  tenacious 
mat  of  bituminous  material  and  stone.  Experience  shows  that 
this  should  not  be  applied  until  the  road  has  seasoned  for  a  few 
months.  If  the  road  is  finished  late  in  the  fall,  so  that  no  oppor- 
tunity will  be  afforded  for  it  to  season  before  winter  closes  down 
construction  work,  the  surface  can  be  bound  with  calcium  chlo- 
ride to  hold  it  until  spring,  when  the  bituminous  mat  can  be 
applied. 

The  ordinary  method  of  maintaining  the  road  is  to  clean  it 
thoroughly  and  then  apply  a  road  oil  uniformly  over  the  surface. 
Some  of  these  oils  are  so  thin  that  they  soak  into  the  surface 
while  others  must  be  covered  with  sharp  sand  or  screenings  free 
from  dust.  The  methods  of  doing  the  work  are  explained  in 
the  chapter  on  surface  applications. 


ROAD  BUILDING  ROCKS 

Mineral  Composition.1 — Reports  of  geologists  and  mineralo- 
gists on  road-building  rocks  classify  them  according  to  their 
origin  as  igneous,  sedimentary  and  metamorphic. 

Igneous  rocks  are  those  which  have  solidified  from  a  very  hot 
liquid  condition  and  their  physical  condition,  technically  termed 
"structure,"  depends  largely  on  the  rate  of  cooling  of  the  fused 
material.  The  "intrusive"  or  "plutonic"  type  of  igneous  rocks 
cooled  slowly  at  great  depths  below  the  earth's  surface,  and  the 
minerals  composing  it  are  usually  in  large  and  well  developed 
particles.  This  type  includes  granite,  syenite,  diorite,  gabbro, 
and  peridotite.  The  "extrusive"  or  "volcanic"  types  of  igneous 
rocks  cooled  more  rapidly  upon  the  earth's  surface  and  are  finer 
grained.  They  frequently  show  a  so-called  "porphyritic" 
structure  on  account  of  the  presence  of  larger  crystals  in  a  fine- 
grained, dense  mass  forming  the  main  mass  of  the  rock.  This 
type  includes  rhyolite,  trachyte,  andesite,  basalt  and  diabase. 

Sedimentary  rocks  are  made  up  of  fragments  of  minerals  or 
shells  that  were  moved  about,  mainly  by  water,  and  finally  de- 
posited on  the  beds  of  lakes  or  seas  in  more  or  less  parallel  layers. 
There  they  became  cemented  together  by  the  pressure  upon  them 
and  changes  in  the  composition  of  a  part  of  their  constituents. 
This  last  change  is  of  the  same  general  nature  as  that  occurring 
far  more  quickly  in  the  case  of  plaster  or  mortar.  This  class 
includes  calcareous  types  of  rock  like  limestone  and  dolomite, 
and  siliceous  types  like  shale,  sandstone,  and  chert  (flint).  Both 
types  are  usually  distinctly  bedded  or  stratified. 

Metamorphic  rocks  were  produced  from  the  two  classes  just 
mentioned  by  pressure  and  heat.  The  long-continued  shearing 
and  compressive  forces  sometimes  produced  a  "foliated"  or 
"schistose"  character,  with  a  parallel  arrangement  of  the  minerals 
composing  them,  or  a  "massive"  or  "nonfoliated"  character. 
Gneiss,  schist  and  amphibolite  are  foliated  metamorphic  rocks, 
and  slate,  quartzite,  eclogite  and  marble  are  nonfoliated  meta- 
morphic rocks. 

1  Abridged  from  Bulletin  348,  U.  S.  Department  of  Agriculture,  "Rela- 
tion of  Mineral  Composition  and  Rock  Structure  to  the  Physical  Prop- 
erties of  Rock  Materials,"  by  E.  C.  E.  Lord,  petrographer,  Office  of  Public 
Roads  and  Rural  Engineering. 

75 


76 


AMERICAN   HIGHWAY   ASSOCIATION 


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ROAD   BUILDING   ROCKS 


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AMERICAN   HIGHWAY   ASSOCIATION 


ROAD    BUILDING   ROCKS  83 

The  original  mineral  components  of  igneous  rocks  and  the 
essential  part  of  metamorphic  schists  are  quartz,  plagioclase, 
orthoclase,  augite,  hornblende,  muscovite,  biotite,  rock  glass, 
magnetite  and  garnet.  These  are  called  primary  minerals. 
Rock  glass,  included  among  them,  is  a  mineral  of  variable  com- 
position found  in  certain  volcanic  rocks  which  cooled  very  rapidly. 
It  is  extremely  brittle  and  when  present  in  appreciable  quantities 
has  a  tendency  to  lower  the  wearing  properties  of  the  rock.  Orth- 
oclase and  plagioclase  are  usually  called  "  feldspar"  by  engineers 
and  biotite  and  muscovite  are  called  "mica." 

Quartz  is  the  most  widely  distributed  mineral  known.  It  has 
a  specific  gravity  of  2.66  and  a  hardness  of  7  in  Mohs'  scale.1 
When  present  in  large  quantities,  especially  when  finely  consoli- 
dated, as  in  fine-grained,  igneous  and  massive  metamorphic 
rocks,  the  resulting  material  is  extremely  hard  and  offers  great 
resistance  to  wear. 

Orthoclase  and  plagioclase  are  among  the  principal  ingredients 
of  igneous  and  metamorphic  rocks  and  some  sandstones.  Their 
specific  gravity  is  2.54  to  2.76  and  their  hardness  6  to  6.5.  Many 
coarse-grained  feldspathic  rocks  break  down  readily  under  im- 
pact on  account  of  the  cleavage  of  these  minerals.  In  fine- 
grained rocks  the  effect  of  this  cleavage  is  less  marked,  and  some 
of  them  are  extremely  hard  and  tough. 

Augite  and  hornblende  are  the  chief  iron-bearing  or  dark  silicate 
constituents  of  basic  igneous  rocks,  commonly  called  "trap 
rocks,"  and  the  crystalline  schists  derived  from  them.  Their 
specific  gravity  is  2.93  to  3.71  and  their  hardness  5  to  6.5.  Their 
crystalline  shape  is  such  that  they  interlock  very  compactly  with 
other  minerals,  which  is  one  of  the  reasons  for  the  marked  dura- 
bility of  trap  rocks. 

Biotite  and  muscovite  occur  chiefly  in  granite,  gneiss  and  mica- 
ceous schist.  Their  specific  gravity  is  2.7  to  3.2  and  their  hard- 
ness is  2  to  3.  The  flaky  character  of  mica  is  well  known  and  is 
largely  responsible  for  the  foliated  character  of  many  metamor- 
phic rocks  and  their  resulting  inferior  wearing  properties  in  roads. 

Magnetite  has  a  specific  gravity  of  5.18  and  a  hardness  of  5.5. 
Garnet  has  a  specific  gravity  of  3.15  and  a  hardness  of  7.5.  They 
occur  in  only  two  road-building  rocks,  peridotite  and  eclogite, 
and  in  some  cases  materially  increase  the  wearing  properties  of 
the  rock. 

Secondary  minerals  are  produced  by  the  alteration  of  rocks, 
mainly  by  the  chemical  action  of  water  and  carbonic  acid  on 
primary  rock  constituents.  The  chief  secondary  minerals  are 

1  Mobs'  scale  of  the  relative  hardness  of  minerals  is  as  follows:  1,  Talc; 
2,  gypsum;  3,  calcite;  4,  fluorite;  5,  apatite;  6,  orthoclase;  7,  quartz;  8, 
topaz ;  9,  corundum ;  10,  diamond. 


84  AMERICAN   HIGHWAY   ASSOCIATION 

calcite,  dolomite,  kaolin,  chlorite,  epidote,  limonite,  serpentine, 
talc,  zeolite  and  opal. 

Calcite  has  a  specific  gravity  of  2.6  and  a  hardness  of  3.  Dolo- 
mite has  a  specific  gravity  of  2.9  and  a  hardness  of  3.5.  These 
two  minerals  are  the  chief  constituents  of  limestones  and  dolo- 
mites, and  cannot  be  distinguished  microscopically.  They 
cleave  freely  and  hence  many  calcareous  rocks  break  down  readily 
when  used  in  roads. 

Kaolin  is  derived  to  a  large  extent  through  the  decomposition 
of  orthoclase.  It  sometimes  occurs  in  small  crystal  flakes  re- 
sembling white  mica  (muscovite),  and  sometimes  as  minute 
grains  of  very  indefinite  composition.  In  the  latter  form,  called 
"amorphous,"  kaolin  has  a  great  effect  on  the  binding  property 
of  rock  powders,  for  it  becomes  glue-like  when  wet,  and  when 
dry  it  binds  together  firmly  the  other  mineral  particles  with 
which  it  is  associated. 

Chlorite  and  epidote  are  derived  from  augite,  hornblende, 
biotite  and  plagioclase  and  are  most  abundant  in  trap  rocks  and 
dark  crystalline  schists.  Chlorite  is  a  soft  green  mineral  which 
occurs  either  in  mica-like  flakes  or  as  very  fine  scales  and  fibers  of 
indefinite  composition.  In  the  latter  form  it  has  cementing 
properties  like  those  of  amorphous  kaolin.  Epidote  (specific 
gravity,  3.25-3.5;  hardness,  6-7)  occurs  as  yellowish  green  crystals 
which,  when  present  in  appreciable  quantities,  apparently  in- 
crease the  wearing  properties  of  rocks. 

The  results  of  a  study  of  several  hundred  road-building  rocks 
indicate  that  the  effects  of  their  mineral  composition  on  their 
value  for  highway  purposes  are  probably  as  follows : 

Igneous  and  nonfoliated  metamorphic  rocks,  owing  to  a  pre- 
ponderance of  hard  silicate  minerals  combined  with  greater  uni- 
formity in  structure,  are  more  durable  than  other  road-making 
materials,  finer-grained  varieties  offering  greater  resistance  to 
abrasion  than  coarse-grained  types. 

The  resistance  to  wear  of  igneous  and  metamorphic  rocks, 
containing  an  abundance  of  quartz,  hornblende,  augite,  epidote, 
and  garnet,  is  greater  than  that  of  similar  rocks  rich  in  mica, 
chlorite,  serpentine,  and  calcite. 

Foliated  metamorphic  rocks,  owing  to  the  parallel  arrange- 
ment of  their  mineral  constituents,  are,  as  a  rule,  deficient  in 
toughness  and  therefore  not  well  adapted  to  road  construction. 

Sedimentary  rocks  are  usually  deficient  in  wearing  properties, 
except  in  the  case  of  highly  indurated  sandstones,  containing  a 
moderate  amount  of  siliceous  clay,  cement,  and  limestones  or 
dolomites  rich  in  quartz  and  having  very  little  clay. 

Rocks  for  road  making  break  down  under  impact  into  frag- 
ments, the  shape  and  physical  character  of  which  are  conditioned 
by  mineral  composition  and  structure. 


ROAD    BUILDING   ROCKS  85 

The  effect  of  weathering  is  generally  to  lower  the  resistance  to 
wear  of  road  materials,  owing  to  the  development  of  soft,  in 
part  glue-like  (colloidal)  products  of  alteration.  Where  the 
secondarjr  minerals  are  harder  and  more  crystalline  the  wearing 
properties  of  the  rocks  are  proportionately  increased. 

The  cementing  value  of  road  materials  is  conditioned  chiefly  by 
the  glue-like  (colloidal)  products  of  rock  decay  and  increases  in  a 
general  way  proportionately  with  these  products,  reaching  a 
maximum  in  rocks  free  from  quartz. 

The  slaking  property  of  rock  powders  is  dependent  in  the  case 
of  siliceous  igneous  and  metamorphic  rocks  chiefly  on  the  physical 
character  of  the  primary  mineral  components,  whereas  in  basic 
igneous  rocks  and  sandstones  it  is  caused  to  a  large  degree  by 
glue-like  (colloidal)  products  of  rock  decomposition. 

Physical  Properties.1 — The  success  or  failure  of  a  rock  for  road 
building  depends  largely  upon  the  extent  to  which  it  will  resist 
the  destructive  influences  of  traffic.  The  three  most  important 
physical  properties  are  hardness,  toughness,  and  binding  power 
Hardness  is  the  resistance  which  the  rock  offers  to  the  displace- 
ment of  its  surface  particles  by  abrasion;  toughness  is  the  resist- 
ance which  it  offers  to  fracture  under  impact;  and  binding  power 
is  the  ability  which  the  dust  from  the  rock  possesses,  or  develops 
by  contact  with  water,  of  binding  the  large  rock  fragments  to 
gether.  In  order  to  approximate  as  closely  as  possible  in  the 
laboratory  the  destructive  effects  produced  by  traffic,  climatic 
agencies  and  faulty  construction,  certain  physical  tests  have 
been  developed. 

Hardness  is  determined  by  subjecting  a  cylindrical  rock  core  25 
millimeters  in  diameter,  drilled  from  the  specimen  to  be  examined, 
to  the  abrasive  action  of  quartz  sand  fed  upon  a  revolving  steel 
disk.  The  end  of  the  specimen  is  worn  away  in  inverse  ratio  to 
its  hardness,  and  the  amount  of  loss  is  expressed  in  the  form  of  a 
coefficient  as  follows: 

Coefficient  of  hardness  =  20  —  w/3,  where  w  equals  the  loss  in 
weight  after  1,000  revolutions  of  the  disk. 

Toughness  is  determined  by  subjecting  a  cylindrical  test  speci- 
men 25  by  25  millimeters  in  size  to  the  impact  produced  by  the 
fall  of  a  2-kilogram  hammer  upon  a  steel  plunger  whose  lower 
end  is  spherical  and  rests  upon  the  test  piece.  The  energy  of 
the  blow  delivered  is  increased  by  increasing  the  height  of  fall 
of  the  hammer  1  centimeter  after  each  blow.  The  height  of 
blow  in  centimeters  at  failure  of  the  specimen  is  called  the  tough- 
ness. 

Abstracted  from  Bulletin  370,  U.  S.  Department  of  Agriculture,  "Re- 
sults of  Physical  Tests  of  Road  Building  Rock/'  by  Pre"vost  Hubbard, 
chemical  engineer,  and  Frank  H.  Jackson,  Jr.,  assistant  chemical  engineer, 
Office  of  Public  Roads. 


86  AMERICAN   HIGHWAY   ASSOCIATION 

A  test  devised  by  the  French  and  sometimes  called  the  Deval 
test,  for  measuring  the  combined  action  of  abrasion  and  impact, 
is  as  follows:  Five  kilograms  of  freshly  broken  rock  between  2 
and  2|  inches  in  size  is  tested  in  a  special  form  of  cylinder  so 
mounted  on  a  frame  that  the  axis  of  rotation  of  the  cylinder  is 
inclined  at  an  angle  of  30°  with  the  axis  of  the  cylinder  itself. 
The  fragments  of  rock  forming  the  charge  are  thus  thrown  from 
end  to  end  twice  during  each  revolution,  causing  them  to  strike 
and  rub  against  each  other  and  the  sides  of  the  cylinder.  After 
10,000  revolutions  the  resulting  material  is  screened  through  a 
-j^-inch  sieve  and  the  weight  of  the  material  passing  is  used  to 
calculate  the  percentage  of  wear.  The  French  coefficient  of 
wear  is  calculated  from  the  per  cent  of  wear  as  follows: 

French  coefficient  of  wear  =  40  H-  percentage  of  wear 

To  determine  the  binding  power,  or  cementing  value,  as  it  is 
usually  called,  500  grams  of  the  material  to  be  tested  is  crushed 
to  pea  size  and  ground  with  water  in  a  ball  mill  until  it  has  the 
consistency  of  a  stiff  dough.  It  is  then  molded  into  cylindrical 
briquettes  25  by  25  millimeters  in  size,  which,  after  thorough 
drying,  are  tested  to  destruction  in  a  special  form  of  impact 
machine.  A  1-kilogram  hammer  falls  through  a  constant  height 
of  1  centimeter  upon  an  intervening  plunger,  which  in  turn  rests 
upon  the  test  piece.  A  graphic  record  of  the  number  of  blows 
required  to  destroy  the  specimen  is  obtained.  The  number  of 
blows  producing  failure  is  called  the  cementing  value  of  the 
material. 

The  specific  gravity,  weight  per  cubic  foot,  and  the  water 
absorption  in  pounds  per  cubic  foot  are  obtained  on  samples  of 
rock  which  are  tested  to  determine  their  road-building  qualities. 
The  weight  per  cubic  foot  is  calculated  from  the  specific  gravity 
of  the  material  obtained  on  a  10-gram  sample  by  the  usual  dis- 
placement method.  The  gain  in  weight  of  this  fragment  after 
four  days'  continuous  immersion  in  water  is  used  to  calculate 
the  water  absorption  in  pounds  per  cubic  foot  of  the  solid  rock. 

Results  of  Tests. — Because  of  the  fact  that  the  various  rock 
families,  when  subjected  to  the  tests  outlined,  give  results  which 
are  more  or  less  distinctive  of  a  group  or  type,  these  results  can 
best  be  discussed  in  many  cases  collectively.  There  are  14  fam- 
ilies of  rock  which  are  more  or  less  commonly  used  in  macadam- 
road  construction.  The  variations  which  have  been  found  to 
exist  in  the  three  principal  tests  for  each  of  these  are  shown  in 
graphic  form  in  the  diagrams  on  pages  76-82.  The  values  of 
the  tests  are  arranged  as  abscissae,  with  the  zero  points  to  the 
left  and  the  values  numerically  increasing  toward  the  right. 


ROAD   BUILDING   BOCKS  87 

The  ordinates  or  vertical  lines  represent  the  percentages  of  the 
total  number  of  samples  having  values  corresponding  to  the 
abscissae  on  which  they  are  plotted.  The  figures  in  parentheses 
hi  the  upper  right-hand  corner  of  each  block  represent  the  total 
number  of  determinations  from  which  these  percentages  were 
calculated. 

Andesite,  Basalt,  Diabase,  Diorite,  Gabbro,  and  Rhyolite 
comprise  the  well-known  group  of  road-building  rocks  commonly 
known  as  "trap."  The  average  toughness  of  all  the  traps,  with 
the  exception  of  gabbro,  which  runs  somewhat  lower,  is  about  18. 
This  is  a  considerably  higher  average  than  that  shown  by  any 
of  the  other  types  or  groups.  The  same  relationship  holds  true 
in  the  abrasion  test,  the  average  French  coefficient  of  wear  run- 
ning from  about  13  to  15.  Comparatively  slight  variations  in 
hardness  are  noted  for  any  family  or  for  the  group  as  a  whole, 
the  average  hardness  for  which  is  about  18.  The  binding  power 
of  the  traps  varies  through  wide  limits,  depending  largely  on  the 
degree  of  weathering  they  have  undergone.  The  specific  gravity 
of  this  group  averages  about  2.9,  giving  an  average  weight  per 
cubic  foot  of  180  pounds.  Individual  samples  are  seldom  less 
than  2.7  nor  more  than  3.2  specific  gravity.  Water  absorption 
may  vary  from  a  few  hundredths  of  1  per  cent  to  over  7  per  cent. 

Granite  is  characterized  by  low  toughness  and  high  hardness. 
The  average  value  for  the  former  is  about  8,  while  that  for  the 
latter  runs  as  18.5.  The  abrasion  test  develops  an  average 
French  coefficient  of  wear  of  about  11.  Cementing  values  run 
low,  the  only  exceptions  being  very  highly  weathered  material 
which  usually  shows  low  toughness  and  resistance  to  wear.  The 
specific  gravity  averages  2.7.  The  weight  per  cubic  foot  aver- 
ages 168  pounds.  Water  absorption  has  been  found  to  run  from 
about  0.04  to  3  per  cent. 

The  limestones  and  dolomites,  or  magnesium  limestones,  are 
undoubtedly  the  most  widely  used  road-building  rock.  The 
average  French  coefficient  of  wear  is  about  8,  toughness  7,  and 
hardness  15.  The  cementing  values  are  usually  good,  about  75 
per  cent  of  all  samples  tested  running  over  25.  The  specific  grav- 
ity of  the  limestones  and  dolomites  averages  close  to  2.7.  In 
general,  the  weight  per  cubic  foot  will  average  about  168  pounds 
for  the  limestones  and  170  pounds  for  the  dolomite.  Absorption 
may  vary  from  a  few  hundredths  of  1  per  cent  to  over  13  per 
cent. 

The  sandstones  are  characterized  by  wide  variations  in  the 
results  of  all  tests.  The  average  French  coefficient  of  wear  is 
about  12,  average  toughness  about  10,  and  average  hardness 
about  16.  The  cementing  value  of  sandstones  varies  widely, 
depending  upon  their  composition.  Their  specific  gravity  aver- 


88  AMERICAN   HIGHWAY   ASSOCIATION 

ages  2.62.  The  weight  per  cubic  foot  averages  164  pounds. 
Absorption  runs  from  a  few  hundredths  of  1  per  cent  to  about  2 
per  cent. 

The  average  toughness  of  marble  is  about  5  and  thev  average 
hardness  is  less  than  14.  Marbles  usually  show  good  cementing 
value  tests,  with  about  the  same  range  as  the  limestones  and 
dolomites.  The  specific  gravity  ordinarily  falls  between  2.7  and 
2.9  and  the  weight  per  cubic  foot  averages  173  pounds,  which  is 
somewhat  higher  than  the  average  for  either  limestone  or  dolo- 
mite. The  maximum  absorption  is  under  2.5  per  cent. 

Quartzites  show  an  average  toughness  of  15.  The  quartzites 
invariably  show  a  low  cementing  value.  Their  specific  gravity 
usually  lies  between  2.6  and  2.8  and  their  average  weight  per  cubic 
foot  is  about  167  pounds.  Their  water  absorption  runs  from  a 
few  hundredths  of  1  per  cent  to  nearly  3  per  cent. 

Gneiss  and  schist  show  similar  physical  properties.  The 
average  French  coefficient  of  wear  for  the  gneiss  samples  is  about 
9.  Their  average  hardness,  toughness,  specific  gravity,  weight 
per  cubic  foot,  and  absorption  are  approximately  the  same  as  for 
granite. 

The  schists  show  an  average  French  coefficient  of  wear  of  about 
12.  Their  average  hardness  is  about  17.5  and  their  toughness 
averages  11.  The  toughness  test  for  both  gneiss  and  schist  is 
made  perpendicular  to  the  plane  of  foliation.  If  taken  hori- 
zontal to  the  plane  of  foliation  much  lower  results  would  be  ob- 
tained, as  failure  would  then  occur  along  these  natural  lines  of 
cleavage.  The  specific  gravity  of  schists  usually  lies  between 
2.65  and  2.90  and  the  average  weight  per  cubic  foot  is  about  181 
pounds.  Water  absorption  is  seldom  over  2  per  cent  for  this 
family. 

With  the  exception  of  the  highly  altered  varieties,  both  gneisses 
and  schists  show  a  rather  low  cementing  value. 

Chert  is  a  very  hard  material,  but  frequently  shows  a  low  re- 
sistance to  wear,  owing  to  its  tendency  to  fracture  along  lines 
which  have  developed  as  shrinkage  cracks  in  the  rock  structure. 
For  this  reason  it  is  extremely  difficult  to  test  for  toughness.  The 
cementing  value  of  pure  chert  is  usually  low,  but  some  highly 
weathered  deposits  develop  in  service  good  cementing  value, 
especially  if  a  high-binding  clay  is  associated  with  it.  The 
French  coefficient  of  wear  has  usually  been  found  to  average  5, 
toughness  16,  and  the  hardness  coefficient  between  19  and  20. 
Specific  gravity  usually  lies  between  2.4  and  2.65  and  the  aver- 
age weight  per  cubic  foot  is  about  160  pounds.  Water  absorp- 
tion may  run  from  a  few  tenths  of  1  per  cent  to  over  8  per  cent. 

Shales  and  slates  are  highly  laminated  rocks  that  tend  to  break 
into  flat  plates  not  suitable  for  road-building  purposes.  They 


ROAD   BUILDING  ROCKS  89 

are  seldom  used  in  road  construction,  except  perhaps  as  a  filling 
for  sub-foundations.  They  vary  greatly  in  nearly  all  of  their 
physical  properties. 

Many  varieties  of  slag  resemble  in  certain  outward  respects 
the  common  road-building  rocks.  However,  in  general,  they 
are  more  porous  and  glassy,  and  vary  so  greatly  in  physical 
properties  that  with  reference  to  their  physical  characteristics 
from  the  standpoint  of  road  construction  they  cannot  well  be 
considered  as  a  single  class  with  definite  limits  or  general  average 
numerical  values. 


CONCRETE  ROADS 

Although  concrete  pavements  were  laid  at  Belief  ontaine,  Ohio, 
in  1893  and  1894,  the  type  did  not  attract  general  attention  until 
fifteen  years  later.  During  1913,  over  10,000,000  square  yards 
were  laid,  eight  times  as  much  as  in  1911.  This  rapid  develop- 
ment was  accompanied  by  marked  differences  in  methods  of  con- 
struction, which  aroused  some  apprehension  that  poor  results 
from  inferior  methods  would  retard  the  logical  adoption  of  the 
type  in  places  for  which  it  was  suited.  Accordingly  road  and 
street  engineers  and  contractors  from  all  parts  of  the  country 
met  in  February,  1914,  for  a  three-day  discussion  of  concrete 
road  building.  The  report  of  this  conference  exercised  a  standard- 
izing influence  on  methods  of  construction,  as  had  the  somewhat 
earlier  adoption  by  the  American  Concrete  Institute  of  stand- 
ard specifications  for  concrete  roads  and  pavements.  Some  of 
the  methods  of  construction  presented  features  which  required 
detailed  investigation,  and  committees  were  appointed  for  such 
work.  In  February,  1916,  a  second  national  conference  was 
held,  at  which  the  reports  of  these  committees  were  received 
and  discussed.  This  chapter  summarizes  the  information  pre- 
sented at  that  conference. 

Foundation  and  Subgrade 

The  following  opinions  regarding  foundations  and  subgrade 
were  adopted  by  the  1916  conference: 

When  roadways  are  constructed  over  fills,  extreme  care  should  be  ob- 
served to  insure  the  use  of  proper  materials  in  layers  of  such  thickness 
that  they  may  be  thoroughly  compacted  so  that  when  the  fill  is  completed 
there  will  be  a  minimum  of  settlement.  In  general,  fills  shall  be  made  in 
thin  layers,  the  depth  depending  on  the  character  of  material  to  be  used 
in  making  the  fill.  The  fill  should  be  allowed  to  stand  for  as  long  a  time 
as  possible,  giving  it  an  opportunity  to  settle  thoroughly  before  the  pave- 
ment is  placed  thereon.  Deep  fills  should  be  allowed  to  settle  through 
one  winter  wherever  such  procedure  is  possible.  Puddling  will  be  found 
advantageous  in  compacting  deep  fills.  Wetting  and  rolling  shall  be  per- 
formed when  making  a  fill  in  order  to  secure  thorough  compactness.  Fills 
should  never  be  made  with  frozen  materials  nor  with  lumps  greater  than  6 
inches  in  their  greatest  dimension. 

The  fundamental  requirement  of  the  subgrade  is  that  it  should  be  of 
uniform  density  so  that  it  will  not  settle  unevenly  and  cause  cracks  in  the 
surface  of  the  pavement.  No  part  of  the  work  is  more  worthy  of  intelli- 

90 


CONCRETE   ROADS  91 

gent  care  and  painstaking  labor  than  the  preparation  of  the  subgrade.  The 
slight  additional  cost  necessary  to  insure  good  results  is  abundantly  jus- 
tifiable. When  the  pavement  is  constructed  on  virgin  soil,  care  should 
be  taken  to  remove  all  soft  spots  so  as  to  insure  a  uniform  density;  and  if 
constructed  on  an  old  roadbed,  even  greater  care  must  be  taken  to  secure 
uniform  density,  as  the  subgrade  is  likely  to  be  more  compact  in  the  cen- 
ter than  at  the  sides.  An  old  roadbed  should  be  scarified,  reshaped  and 
rolled.  The  subgrade  adjacent  to  curbs  should  be  hand-tamped. 

The  importance  of  a  uniformly  firm  support  for  the  concrete 
slab  was  not  fully  appreciated  by  all  roadbuilders.  There  was  an 
opinion  among  some  that  the  concrete  would  act  as  a  beam  and 
distribute  the  loads  coming  on  it  over  such  a  wide  area  that  inequali- 
ties in  the  sustaining  power  of  the  earth  would  prove  unimportant. 
The  number  of  cracks  in  concrete  pavements  attributable  to  un- 
warranted confidence  in  this  beam  action  is  beyond  proof,  but 
today  the  opinion  is  generally  held  that  the  money  spent  in  se- 
curing a  firm  foundation  is  a  wise  outlay  to  insure  low  mainte- 
nance charges.  This  is  particularly  the  case  where  an  old  road 
is  used  for  a  foundation.  It  is  unlikely  that  a  concrete  pavement 
will  be  laid  on  it  until  the  old  road  needs  repairs.  If  the  sur- 
face is  then  merely  leveled  by  a  thin  course  of  stone  or  gravel,  it 
is  possible  that  there  will  be  weak  places,  particularly  along  the 
sides  of  the  road. 

Drainage 

The  1916  conference  adopted  the  following  statement  of  the 
principles  which  should  govern  the  drainage  of  the  roadbed  sup- 
porting a  concrete  slab: 

The  drainage  of  the  roadbed  is  of  vital  importance.  If  the  subgrade 
is  not  well  drained  there  is  danger  of  unequal  settlement  and  of  frost  action, 
which  will  cause  cracks.  The  method  of  drainage  to  be  used  will  depend 
on  local  conditions.  For  streets,  as  well  as  roads,  tile  drains  may  be  used 
which  should  be  laid  on  each  side  of  the  roadway,  or  on  one  side  only, 
with  cross-drains  leading  thereto  at  a  suitable  depth,  depending  on  the 
width  of  the  pavement.  Drainage  trenches,  if  placed  under  the  subgrade, 
should  be  completed  before  final  rolling. 

There  is  an  objection  to  the  use  of  cross-drains  under  thin 
concrete  roads  which  is  not  serious  in  most  cases  but  may  be 
under  some  conditions.  It  is  practically  impossible  to  compact 
the  material  over  a  blind  drain  as  thoroughly  as  that  of  the  main 
portion  of  the  subgrade,  and  each  blind  drain  is  likely  to  be  a  weak 
place  in  the  foundation.  An  alternative  for  them  which  some 
engineers  have  advised  is  the  construction  of  a  blind  drain  just 
outside  each  edge  of  the  concrete  slab  and  extending  8  or  10 
inches  below  the  subgrade.  These  drains  are  connected  every 
50  feet  with  the  side  ditches  by  blind  drains.  All  drains  under 


92  AMERICAN   HIGHWAY   ASSOCIATION 

the  roadway  should  have  a  covering  of  sand  or  fine  gravel  on 
top  to  prevent  the  mortar  in  the  wet  concrete  from  passing  into 
the  broken  stone  or  gravel  of  the  drain. 

Cross-section  of  Roads 

The  following  statements  were  adopted  by  the  1916  conference 
regarding  the  section  of  the  concrete  pavement : 

The  thickness  of  a  concrete  road  or  pavement  is  controlled  by  many 
factors,  each  of  which  should  be  given  consideration.  In  view  of  the  in- 
creasing use  of  the  heavy  motor  truck  and  bus,  it  seems  unwise  to  build 
pavements  with  a  thickness  of  less  than  six  inches  at  any  point.  In  gen- 
eral, pavements  should  be  thicker  at  the  center  than  at  the  sides.  Alleys 
with  an  inverted  crown,  and  narrow  one-slope  roads,  should  have  a  uni- 
form thickness.  Wherever  the  thickness  can  be  increased  without  excess- 
ive cost,  to  secure  a  flat  subgrade,  or  one  nearly  flat,  such  increase  is 
advisable. 

The  desirable  width  for  single-track  roads  is  10  feet.  The  desirable 
width  of  double-track  roads  is  18  feet.  The  total  width  of  the  roadway 
should  not  be  less  than  20  feet  for  single-track  roads  and  not  less  than  26 
feet  for  double-track  roads. 

The  crown  of  roads  and  pavements  should  be  not  less  than  one  one- 
hundredth  nor  more  than  one-fiftieth  of  the  total  width.  Except  in  un- 
usual cases,  one  one-hundredth  will  be  sufficient  for  country  roads  and  one- 
fiftieth  will  be  considered  satisfactory  for  alley  pavenents.  For  city 
streets  an  average  crown  of  one -seventy-fifth  will  generally  be  found 
sufficient  and  should  not  be  reduced,  except  on  grades. 

Single-track  concrete  roads  are  occasionally  built  on  the  right- 
hand  side  of  the  roadway  going  in  the  direction  of  the  heavy 
traffic.  This  gives  the  loaded  wagons  the  better  surface.  The 
templet  used  in  determining  the  section  of  the  road  is  the  same 
as  for  a  double-track  road  but  only  one-half  the  road  is  concreted. 
In  Huron  and  Medina  Counties,  single-track  roads  have  been 
built  as  one-slope  roads  instead  of  half  the  section  of  double-track 
roads,  and  this  construction  is  preferred  by  some  engineers. 

In  Wayne  County,  Michigan,  it  has  been  decided  to  make 
concrete  roads  18  feet  wide  wherever  possible,  and  never  less 
than  16  feet.  Near  Detroit  the  width  will  be  20  feet.  While 
this  increase  in  width  from  10,  12,  15,  and  16  feet  will  add 
materially  to  the  first  cost,  it  is  expected  to  prove  economical 
in  the  long  run,  because  the  expense  of  maintaining  heavy  broken 
stone  or  gravel  shoulders  will  be  avoided.  This  maintenance  is  a 
large  sum  on  comparatively  narrow  roads  with  heavy  traffic. 

There  is  a  decided  difference  of  opinion  regarding  shoulders 
for  concrete  roads.  Some  engineers  hold  that  the  natural  soil 
should  be  used,  and  where  satisfactory  shoulders  cannot  be 
made  of  it  the  width  of  the  concrete  should  be  increased.  Other 
engineers  recommend  gravel  or  broken  stone  shoulders  after 


CONCRETE   ROADS  93 

experience  with  them.  The  difference  of  opinion  is  probably 
due  to  differences  in  the  quality  of  the  earth  which  must  be 
used  for  earth  shoulders  and  to  differences  in  the  character  of  the 
traffic,  upon  which  the  opinions  are  based.  There  is  no  question, 
however,  that  if  traffic  makes  frequent  use  of  shoulders  of  clay 
or  clayey  loam,  they  are  speedily  ruined,  and  if  heavy  traffic  makes 
frequent  use  of  macadam  shoulders,  the  junction  between  the 
concrete  and  broken  stone  becomes  a  long  rut.  In  either  case  the 
proper  maintenance  of  the  shoulders  will  be  expensive.  If  two 
macadam  or  gravel  shoulders  wider  than  4  feet  are  considered 
necessary,  it  is  advisable  in  every  case  to  consider  the  alternative 
of  an  increased  width  of  concrete.  The  construction  of  gravel 
and  macadam  shoulders  should  be  postponed,  if  practicable,  until 
a  month  after  the  concrete  road  has  been  finished,  and  they  should 
be  left  slightly  higher  than  the  concrete  to  facilitate  turning 
out  on  them. 

In  cuts,  where  the  grades  are  over  5  per  cent,  it  is  usually  neces- 
sary to  pave  the  ditches  and  to  use  gravel  or  macadam  shoulders. 
The  maintenance  of  these  ditches  and  shoulders  is  expensive, 
and  it  is  possible  that  money  will  be  saved  in  the  end,  even  on 
single-track  roads,  by  increasing  the  width  of  the  concrete  and 
adding  a  concrete  ditch  and  curb  at  each  side.  The  ordinary 
construction  will  call  for  a  10-foot  concrete  road,  8  feet  of  shoul- 
ders and  8  feet  of  ditches,  a  total  of  26  feet  width  of  cut  at  the 
bottom  of  the  excavation.  For  this  can  be  substituted  a  concrete 
roadway  16  feet  wide  with  two  integral  curbs  bringing  the  total 
width  to  17  feet  8  inches.  The  curb  acts  as  an  abutment  for  the 
toe  of  the  slope. 

On  fills  over  5  or  6  feet  high,  where  turning  out  on  a  soft  shoulder 
may  cause  a  serious  accident,  it  is  desirable  to  widen  a  single- 
track  pavement  to  16  feet  unless  the  top  of  the  fill  is  so  wide  that 
an  overturned  car  will  not  roll  down  the  slope.  In  any  such  case, 
the  safety  of  the  public  requires  a  more  careful  study  of  the 
dangers  on  embankments  than  was  given  to  the  subject  before 
automobiles  became  numerous.  Attention  is  called  to  the 
record  of  deaths  and  injuries  on  page  25. 

Materials 

Cement  is  bought  for  most  road  work  under  the  standard 
specifications  of  the  American  Society  for  Testing  Materials, 
which  were  revised  in  1916.  They  are  printed  in  the  next  chapter. 

The  following  statements  regarding  fine  and  coarse  aggregate 
were  adopted  by  the  1916  conference: 

The  selection  of  proper  aggregates  for  concrete  road  construction  is 
of  utmost  importance.  Clean,  hard,  well-graded  materials  are  absolutely 


94  AMERICAN   HIGHWAY  ASSOCIATION 

essential  to  success.  For  this  reason  samples  of  the  materials  proposed 
for  use  should  be  submitted  to  the  engineer  for  approval  before  orders 
are  placed.  These  samples  should  be  carefully  inspected;  and  if  possible 
laboratory  tests  made  to  determine  their  suitability.  If  laboratory  tests 
on  shipments  cannot  be  made,  field  tests  can  be  used  to  furnish  a  general 
indication  of  quality. 

The  different  aggregates  should  be  kept  clean  and  separate. 

Aggregates  to  be  used  in  the  wearing  course  of  two-course  pavements 
should  never  be  placed  on  the  subgrade  but  on  planks  or  some  other  means 
provided  to  keep  them  free  from  dirt.  When  aggregates  are  placed  di- 
rectly on  the  subgrade  care  should  be  used  by  the  shovelers  to  avoid  get- 
ting clay  or  earth  shoveled  from  the  subgrade  into  the  mix.  Aggregates 
should  not  only  be  clean  when  they  are  delivered  on  the  job,  but  clean 
when  placed  in  the  mixer. 

Investigations  to  determine  the  usefulness  of  the  rattler  test 
to  show  the  value  of  different  concrete  mixtures  for  road  work 
indicate  that  it  may  prove  of  value.  For  the  present,  however, 
the  older  practice  of  relying  on  tests  of  the  stone  is  being  followed 
wherever  any  testing  is  done.  Generally  the  best  clean,  hard  and 
tough  crushed  rock  or  gravel  is  used,  provided  it  will  give  a  con- 
crete harder  than  the  mortar  used  with  it.  It  is  desirable  to 
use  stone  having  a  French  coefficient  of  wear  of  at  least  8. 

Experience  indicates  that  cracks  occur  more  often  in  gravel 
concrete  than  in  stone  concrete.  Probably  this  is  largely  due 
to  the  very  fine  material  on  the  surface  of  most  gravel  pebbles, 
which  must  be  washed  off  carefully  to  make  the  material  fit  for 
road  work. 

Fine  aggregate,  or  "sand,"  is  generally  required  to  pass  a  J- 
inch  screen.  Not  more  than  25  per  cent  must  pass  a  50-mesh 
sieve  and  not  more  than  5  per  cent  a  100-mesh  sieve.  It  must 
contain  no  vegetable  or  other  deleterious  matter  and  not  over  3 
per  cent  by  weight  of  clay  or  loam.  The  sand  should  be  tested 
frequently  in  the  field  by  shaking  a  sample  with  water  in  a  grad- 
uated glass  and  allowing  it  to  settle  for  an  hour.  If  there 
is  more  than  about  5  per  cent  of  very  fine  material  showing  on  the 
top  of  the  sand,  samples  should  be  sent  to  the  laboratory.  Nat- 
ural sand  or  screenings  from  hard,  tough,  durable  rock  may 
be  used.  Natural  sand  sometimes  contains  vegetable  acids 
which  reduce  its  value  for  good  concrete.  Their  presence  is 
determined  by  making  similar  briquettes  of  the  natural  sand 
and  of  standard  Ottawa  sand,  and  no  natural  sand  should  be  used 
in  road  work  which  does  not  give  a  strength  at  least  equal  to 
that  obtained  with  Ottawa  sand.  The  best  sand  is  that  in  which 
the  coarse  particles  predominate.  Improvements  can  sometimes 
be  made  by  mixing  two  natural  sands  or  a  fine  sand  and  screenings. 

The  standard  specifications  for  coarse  aggregate,  or  "stone" 
call  for  material  passing  a  2-inch  round  opening,  with  not  more 


CONCRETE   ROADS  95 

than  5  per  cent  passing  a  screen  having  four  meshes  per  inch 
and  without  any  intermediate  sizes  removed. 

The  water  used  in  making  the  concrete  must  be  free  from  oil, 
acid,  alkali  or  vegetable  matter. 

Proportions 

The  1916  conference  adopted  the  following  statements  of  the 
principles  governing  the  proportions  of  the  materials: 

The  method  of  measuring  materials  for  the  concrete,  including  water, 
should  be  one  which  will  insure  accurate  proportions  of  each  of  the  in- 
gredients at  all  times.  It  is  recommended  that  a  sack  of  Portland  ce- 
ment, containing  94  pounds  net,  be  considered  the  equivalent  to  1  cubic 
foot. 

The  proportions  should  not  exceed  5  parts  of  fine  and  coarse  aggregate 
measured  separately  to  1  part  of  Portland  cement,  and  the  fine  aggregate 
should  not  exceed  40  per  cent  of  the  mixture  of  fine  and  coarse  aggregates. 

The  standard  specifications  for  one-course  country  roads  call 
for  one  sack  of  cement  to  not  more  than  2  cubic  feet  of  fine  aggre- 
gate and  not  more  than  3  cubic  feet  of  coarse  aggregate,  with 
the  volume  of  fine  aggregate  never  less  than  half  that  of  the 
coarse  aggregate.  A  cubic  yard  of  the  mixed  concrete  must 
contain  at  least  1.7  barrels  of  cement.  The  amount  of  water 
used  must  be  enough  to  produce  concrete  holding  its  shape 
when  struck  with  a  template.  Concrete  which  has  partly  hard- 
ened must  never  be  used. 

The  standard  specifications  for  two-course  pavements  call 
for  a  base  mixed  in  the  proportions  of  1  sack  of  cement  to  not 
more  than  2J  cubic  feet  of  fine  aggregate  and  not  more  than  4 
cubic  feet  of  coarse  aggregate,  with  at  least  half  as  much  fine  as 
coarse  aggregate.  Two  grades  of  top  aggregate  are  specified 
for  the  top  course;  No.  1  must  pass  a  $-inch  screen  and  have  not 
over  10  per  cent  passing  a  J-inch  screen,  and  No.  2  must  pass  a 
1-inch  screen  and  have  not  over  5  per  cent  passing  a  J-inch 
screen.  Two  mixtures  are  specified  for  the  top  course.  Mix- 
ture 1  consists  of  one  sack  of  cement  to  not  more  than  1  cubic 
foot  of  fine  aggregate  and  not  more  than  1^-cubic  feet  of  No. 
1  top  aggregate.  Mixture  2  consists  of  one  sack  of  cement 
to  not  more  than  1J  cubic  feet  of  fine  aggregate  and  not  more 
than  2J  cubic  feet  of  No.  2  top  aggregate.  The  volume  of  fine 
aggregate  must  equal  half  the  volume  of  top  aggregate  in  either 
mixture. 

The  quantities  of  cement,  sand  and  gravel  required  to  build 
a  mile  of  road  of  different  widths  and  thicknesses  are  given  in  the 
accompanying  tables,  supplied  by  the  Portland  Cement  Associa- 
tion. They  are  based  on  the  assumption  that  a  barrel  of  cement  is 


96 


AMERICAN   HIGHWAY   ASSOCIATION 


equivalent  to  4  cubic  feet  and  the  voids  in  the  stone  are  45  per 
cent.  Variations  from  the  tabulated  quantities  may  amount 
to  10  per  cent  either  way. 

The  proportions  of  cement,  sand  and  stone  should  be  such 
that  the  concrete  will  have  the  properties  desired  for  a  rpad. 
Where  good  stone  is  expensive  but  softer  stone  is  cheaper,  a  two- 
course  pavement  utilizing  the  poor  stone  in  the  base  and  the  hard 
stone  in  the  top  may  prove  more  economical  than  a  thinner  one- 

Quantities  of  Cement,  Sand  and  Stone  Required  for  One  Mile  of  Single- 
Course  Concrete  Road  of  Different  Widths  and  Thicknesses 

(Furnished  by  the  Portland  Cement  Association) 


1 

THICK- 
NESS 

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SECTION 

SUPER- 
FICIAL 
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2088 

4082 

1220 

1806 

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course  pavement  of  the  harder  stone.  In  any  case  the  amount 
of  mortar  used  should  be  about  10  per  cent  in  excess  of  the  voids 
in  the  stone.  There  is  so  much  variation  in  the  grading  of  sand 
and  stone  that  a  1:2:4  mixture  in  one  place  may  be  equal  to  a 
1:2:3  mixture  in  another.  As  the  work  progresses,  the  quality 
of  the  concrete  must  be  watched  carefully,  and  the  proportions 
shifted  so  that  the  greatest  density  will  be  obtained.  Attention 
to  this  feature  of  the  work  is  considered  very  important  by  ex- 
perienced concrete  road  builders. 


CONCKETE   ROADS 


97 


Quantities  of  Cement,  Sand  and  Stone  ^  in  One  Mile  of  Two-Course  Concrete  Road  of 
Different  Widths  and  Thicknesses 

(Furnished  by  the  Portland  Cement  Association) 


BASE 

• 

BASE  MIX;  1:  2$:  4 

BASE  MIX;  1:2:  4 

TOP 

1 

TOP  MIX;  1$:  2$ 

TOP  MIX;  1:  1:  1} 

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Mixing 

The  principles  that  should  govern  mixing  were  stated  as  fol- 
lows by  the  1916  conference: 

The  ingredients  should  be  mixed  in  a  batch  mixer.  The  mixing  should 
be  continued  for  at  least  one  minute  after  all  the  materials  are  in  the  mixer 
and  before  any  of  the  concrete  is  discharged.  The  speed  of  the  mixer 
should  not  exceed  16  revolutions  per  minute;  however,  the  time  and  not 
the  number  of  revolutions  should  be  the  gage  of  proper  mixing. 

The  practice  is  to  mix  concrete  entirely  too  wet.  The  consistency 
should  be  such  as  not  to  require  tamping,  but  not  so  wet  as  to  cause  the 
separation  of  the  mortar  from  the  aggregate  in  handling  and  placing.  The 
strength  and  wearing  qualities  of  the  concrete  are  vitally  lessened  by  an 
excess  of  water  in  mixing. 

The  reason  for  fixing  one  nvnute  as  the  minimum  time  for 
mixing  is  that  tests  have  shown  that  water  is  not  worked  through 


98  AMERICAN  HIGHWAY  ASSOCIATION 

the  mass  as  it  should  be  in  less  than  a  minute.  A  smaller  quan- 
tity of  wat  r  can  be  used  with  long-time  mix  ng  than  with  short- 
time  mixing  and  the  same  degree  of  fluidity  obtained.  On  ac- 
count of  the  desirability  of  keeping  the  amount  of  water  as  close 
as  possible  to  1  gallon  per  cubic  yard  of  concrete,  at  least  one 
minute  nrxing  time  is  desirable.  If  a  large  quantity  of  water 
is  used  and  the  mixing  time  is  less  than  a  minute,  the  product 
may  appear  uni  orm  to  the  eye  when  it  actually  is  not  well  mixed. 
The  reason  for  restricting  the  speed  of  the  mixer  to  16  revolu- 
tions per  minute  is  that  at  a  higher  speed  some  of  the  material 
sticks  to  the  drum  and  there  is  considerable  splashing  as  the 
concrete  is  discharged.  At  least  10  revolutions  are  necessary 
to  mix  the  aggregate. 

Placing 

The  principles  governing  placing  were  stated  as  follows  by  the 
1916  conference: 

If  the  subgrade  has  been  disturbed  by  teaming  or  other  causes,  it  should 
be  brought  to  its  former  surface,  and  thoroughly  moistened  with  water. 
The  concrete  should  be  deposited  rapidly  to  the  required  depth  and  width. 
The  section  should  be  completed  to  a  transverse  joint,  with  the  use  of 
intermediate  forms  or  bulkheads,  or  a  transverse  joint  may  be  placed  at 
the  point  of  stopping  the  work.  In  case  the  mixer  breaks  down  the  concrete 
should  be  mixed  by  hand  to  complete  the  section.  Where  reinforcement 
is  used  it  should  be  embedded  in  the  concrete  before  the  concrete  has  begun 
to  harden;  the  concrete  above  the  reinforcement  should  be  placed  within 
20  minutes  after  the  placing  of  the  concrete  below. 

In  two-course  pavements  the  top  should  be  placed  within  twenty  min- 
utes after  the  placing  of  the  bottom. 

The  standard  specifications  allow  forty-five  minutes  as  the 
maximum  time  between  the  laying  of  the  bottom  course  and  the 
placing  of  the  top  course. 

Practically  all  concrete  roads  are  built  with  special  paving 
mixers  which  discharge  the  concrete  on  the  road  where  it  is  to 
be  used  by  means  of  chutes  or  buckets  hauled  along  a  boom  that 
can  be  swung  from  one  side  of  the  road  to  the  other.  The  pitch 
of  the  chute  should  be  steep  enough  to  deliver  concrete  of  a 
proper  consistency  readily.  In  the  attempt  to  cover  consider- 
able area,  contractors  sometimes  set  the  chute  at  a  flat  angle 
and  use  too  much  water,  in  order  to  make  the  concrete  flow 
readily.  Tests  have  shown  that  the  least  angle  of  the  chute 
should  be  20  degrees.  If  the  chute  is  new  or  rusted,  concrete 
with  a  proper  amount  of  water  will  flow  rather  slowly  down  a 
20  degree  slope  until  the  metal  surface  has  been  smoothed  by  the 
wet  mass.  For  this  reason  the  chute  may  need  a  steeper  slope 
at  the  outset  than  later. 


CONCRETE   ROADS  99 

Forms 

The  1916  conference  adopted  the  following  statement  of  the 
principles  that  should  govern  the  use  of  forms  to  retain  the  con- 
crete at  the  sides  of  the  roadway: 

Metal  forms  of  sufficient  strength  to  withstand  the  necessary  hard 
usage  are  preferred.  When  wooden  forms  are  used  they  should  be  of  at 
least  2-inch  stock  and  capped  with  a  2-inch  angle  iron,  so  constructed  that 
adjacent  sections  can  be  lapped.  Forms  should  have  a  width  not  less 
than  the  thickness  of  the  pavement  at  the  sides.  Particular  care  should 
be  exercised  to  see  that  the  top  edges  of  forms  are  clean  so  as  to  avoid  un- 
evenness  in  the  finished  pavement.  If  forms  are  warped  or  stakes  not 
properly  placed,  a  poor  alignment  of  the  edge  of  the  concrete  slab  will 
result. 

They  must  be  set  firmly  and  the  topes  must  be  true  to  grade, 
because  they  support  the  templets,  bridges  and  other  appliances 
used  in  finishing  the  surface.  The  steel  angles  on  wood  forms 
are  necessary  to  enable  the  finishing  work  to  proceed  in  a  satis- 
factory manner.  By  having  the  angles  project  3  or  4  inches 
beyond  the  end  of  the  wood  at  one  end  and  set  back  the  same 
distance  at  the  other,  the  alignment  of  the  forms  will  be  facili- 
tated. Painting  wood  forms  will  prevent  warping  and  add  to 
their  life.  Where  a  power-driven  striking  and  finishing  machine 
is  used,  specially  heavy  forms  securely  held  in  place  are  needed. 

Joints 

While  transverse  joints  are  omitted  on  some  work,  they  are 
generally  required  because  of  the  prevailing  opinion  that  they 
reduce  the  cracking  of  the  concrete.  They  are  constructed  by 
placing  across  the  road  a  strip  of  prepared  filler  made  for  the 
purpose.  This  filler  is  usually  held  in  place  by  a  steel  templet 
until  the  concrete  is  deposited  against  it.  The  templet  is  then 
removed  and  the  concrete  settles  against  the  filler.  The  joints 
are  of  two  types,  with  and  without  metal  protection  plates.  The 
following  statements  regarding  them  were  adopted  at  the  1916 
conference : 

Transverse  joints  should  be  placed  across  the  pavement  perpendic- 
ular to  the  center  line  about  50  feet  apart.  There  seems  to  be  a  tendency 
to  lengthen  the  distance  between  joints.  Joints  should  extend  entirely 
through  the  pavement,  as  well  as  through  the  curb  if  integral  curbs  are 
used.  Joints  should  be  constructed  perpendicularly  to  the  surface  of  the 
pavement  to  avoid  the  possibility  of  one  slab  rising  above  the  other. 

The  tendency  of  present  practice  is  toward  the  omission  of  metal 
protection  plates  for  joints.  It  is  possible  that  the  value  of  metal  pro- 
tection plates  is  dependent  somewhat  on  the  character  of  the  aggregate 
used,  and  it  is  considered  that  they  are  more  essential  in  street  pavements 
than  in  country  highways. 


100  AMERICAN  HIGHWAY  ASSOCIATION 

The  standard  specifications  call  for  J-inch  transverse  joints 
at  intervals  of  not  more  than  36  feet.  The  filler  must  project 
at  least  f-inch  above  the  concrete  during  construction,  and  after 
the  completion  of  the  pavement  it  is  trimmed  off  f-inch  above 
the  surface.  The  traffic  flattens  out  the  projecting  material  and 
hardens  the  top  of  the  joints.  Experience  shows  that  it  is  very 
desirable  to  have  the  joints  form  a  plane  surface  perpendicular 
to  the  surface  of  the  road. 

Measurements  of  the  expansion  and  contraction  of  concrete 
roadway  slabs  have  been  made  by  R.  J.  Wig,  C.  S.  Laubly  and 
W.  A.  Mclntyre,  from  which  they  drew  the  following  conclu- 
sions: Contraction  and  expansion  are  caused  by  both  temper- 
ature changes  and  changes  in  moisture  conditions,  and  under 
climatic  conditions  similar  to  those  at  Washington,  D.  C.,  the 
effects  from  these  two  factors  in  concrete  road  surfaces  are  ap- 
proximately of  the  same  magnitude.  In  concrete  roads,  ex- 
pansion and  contraction  are  sufficient  to  cause  frequent  trans- 
verse cracks  unless  joints  are  provided.  The  actual  movement 
in  any  particular  case  depends  upon  the  character  of  the  concrete 
and  of  the  subgrade.  A  sloppy  concrete  shows  greater  movement 
than  a  concrete  mixed  only  moderately  wet. 

Organization  of  the  Work 

In  order  for  the  work  to  proceed  economically,  it  is  necessary 
for  the  mixer  to  be  kept  running  most  of  the  time.  This  can 
only  be  accomplished  if  repair  parts  are  kept  on  hand  and  mate- 
rials are  supplied  as  needed.  If  the  materials  are  delivered  by 
rail  it  often  pays  to  keep  men  at  the  sand  and  stone  plants  to  see 
that  the  railroads  furnish  cars  as  needed  and  the  shipments  are 
made  on  time.  If  the  contractor  operates  his  quarry  he  must 
see  that  precautions  are  taken  to  reduce  delays  due  to  break- 
downs or  other  causes  to  a  minimum.  The  delivery  of  mate- 
rials along  the  road  calls  for  careful  planning  of  both  plant  and 
organization.  In  any  case,  provision  should  be  made  against  de- 
lays due  to  insufficient  materials  by  storing  supplies  of  cement, 
sand  and  stone  on  the  work.  The  cement  can  be  stored  in  a  shed 
at  the  railroad  siding  or  in  tents  with  raised  wood  floors  along  the 
road.  The  sand  can  also  be  stored  along  the  road.  The  stone  is 
best  stored  at  the  railroad  siding,  because  it  is  costly  to  rehandle 
and  by  doing  the  work  at  one  place  mechanical  appliances  can  be 
used  which  will  reduce  the  expense  materially.  The  organiza- 
tion should  be  arranged  to  avoid  all  unnecessary  handling  of 
materials,  not  only  because  this  involves  a  labor  charge  but  also 
because  transportation  equipment  is  doing  no  useful  work  while 
being  loaded  or  unloaded.  Tractors  with  trailers,  motor  trucks 


CONCRETE   ROADS  101 

and  industrial  railways  are  generally  used  for  hauling,  and  by 
having  competent  repairmen  to  keep  them  in  order  and  running 
them  with  two  shifts  so  as  to  use  them  about  eighteen  hours  a 
day,  very  low  unit  costs  are  often  obtained  in  comparison  with 
the  expense  of  hauling  by  horses  or  mules. 

The  water  supply  must  be  planned  to  wet  the  subgrade,  sup- 
ply the  mixer  and  keep  the  concrete  wet  for  a  number  of  days 
after  it  is  laid.  While  it  has  been  delivered  along  the  road  in 
tanks,  it  is  usually  pumped  through  a  pipe,  generally  2  inches  in 
diameter.  As  the  water  which  must  be  used  sometimes  con- 
tains sand  which  will  score  the  cylinders  or  plungers  of  a  high 
pressure  pump  so  as  to  put  it  out  of  service,  it  is  often  lifted  by  a 
centrifugal  pump  in  such  cases  into  a  storage  tank  where  the  sand 
has  an  opportunity  to  settle  before  the  water  is  drawn  by  the 
high-pressure  pump.  If  the  tank  has  two  chambers  separated 
by  a  partition  running  nearly  up  to  the  water  level,  the  separa- 
tion of  the  sand  will  be  improved,  for  the  stream  water  can  be 
delivered  into  one  chamber  where  most  of  the  sedimentation 
will  occur  and  be  drawn  from  the  other.  There  should  be  a  relief 
valve  in  the  pipe  line  near  the  pressure  pump  so  as  to  prevent 
breaking  the  pipe  if  all  the  gates  on  it  are  closed.  If  no  valve  is 
used  the  pump  should  be  belt  driven,  so  that  in  case  the  pressure 
rises  the  belt  will  slip.  The  friction  head  in  a  2-inch  pipe  when 
discharging  50  gallons  per  minute  is  about  85  feet  per  1000  feet 
of  its  length,  and  when  discharging  60  gallons  per  minute  the  fric- 
tion head  is  about  115  feet.  Consequently  the  pump  must  have 
power  to  overcome  a  considerable  pressure  due  to  friction  as  well 
as  that  due  to  the  highest  elevation  to  which  the  water  must 
be  raised. 

The  size  of  the  paving  gang  will  depend  upon  the  size  of  the 
mixer,  which  should  depend  in  turn  upon  the  rate  at  which  mate- 
rials can  be  delivered  to  it.  There  are  two1  sizes  of  mixers,  one 
in  which  two  sacks  of  cement  are  used  in  each  batch  of  concrete 
and  the  other  taking  a  three-sack  batch.  The  smaller  machine 
requires  about  two  men  handling  cement,  two  shovelers  and  two 
wheelers  for  sand,  three  shovelers  and  three  wheelers  for  stone, 
a  helper  at  the  mixer  and  a  man  to  bundle  the  cement  sacks. 
The  larger  machine  requires  about  two  men  to  handle  cement, 
three  shovelers  and  three  helpers  for  sand,  four  shovelers  and 
four  wheelers  for  stone,  a  helper  at  the  mixer  and  a  man  to  bundle 
sacks.  In  addition  the  crew  requires  a  foreman,  a  mixer  oper- 
ator, a  fireman,  two  men  setting  forms,  a  pump  tender,  three  or 
four  men  spreading  and  floating  the  concrete,  two  finishers,  and 
one  or  two  attending  to  the  curing  of  the  concrete.  To  keep 

8  During  1916,  four-sack  mixers  were  used  on  several  roads,  so  it  is  prob- 
able that  there  will  be  three  sizes  of  mixers  in  regular  use  soon. 


102  AMERICAN   HIGHWAY   ASSOCIATION 

such  a  gang  working  efficiently  in  the  comparatively  small  area 
occupied  by  a  concreting  job  it  is  necessary  to  have  the  mate- 
rials deposited  so  they  can  be  handled  expeditiously  and  without 
confusion. 

Finishing 

The  principles  which  should  govern  the  finishing  of  concrete 
were  stated  as  follows  by  the  conference: 

The  surface  of  the  concrete  should  be  struck  off  by  means  of  a  templet 
moved  with  a  combined  longitudinal  and  transverse  motion.  The  excess 
material  accumulated  in  front  of  the  templet  should  be  uniformly  distrib- 
uted over  the  surface  of  the  pavement  except  near  the  transverse  joint, 
vrhere  the  excess  material  should  be  removed. 

The  concrete  adjoining  the  transverse  joint  should  be  dense  and  any 
depressions  in  the  surface  should  be  filled  with  concrete  of  the  same  com- 
position as  the  body  of  the  work.  After  being  brought  to  the  established 
grade  with  a  templet,  the  concrete  should  be  finished,  from  a  suitable 
bridge,  with  a  wood  float  to  true  surface.  A  metal  float  should  not  be 
used.1 

Brooming  of  the  surface  is  not  necessary  and  grooves  are  objectionable 
even  on  grades. 

For  country  roads  the  templet  or  strikeboard  is  often  made 
of  two  2  by  10-inch  planks  1  foot  longer  than  the  road  is  wide. 
The  lower  edge  is  cut  to  the  desired  crown  of  the  road  and  shod 
with  a  strip  of  J  by  4-inch  steel  fastened  with  countersunk  screws. 
It  has  a  handle  on  each  side  at  each  end,  so  it  can  be  moved  along 
easily  with  a  kind  of  sawing  motion.  This  motion  fills  all  de- 
pressions with  concrete  and  has  no  tendency  to  drag  out  the 
large  stone.  A  slight  excess  o  .'concrete  is  always  kept  ahead 
of  the  strikeboard,  and  a  workman  often  walks  in  front  of  the 
board  to  spread  the  concrete  and  take  care  of  any  excess  that 
may  accumulate  in  front  of  it.  It  is  usually  necessary  to  run  the 
Btrikeboard  over  the  surface  three  times;  with  very  angular  stone 
it  may  be  necessary  to  go  over  it  four  times. 

Finishing  is  now  regarded  as  very  important.  At  Sioux  City, 
Iowa,  where  the  concrete  streets  are  unusually  free  from  cracks, 
the  success  with  this  type  of  roads  is  attributed  to  the  special  care 
spent  in  the  finishing.  A  wood  float  is  preferred  to  a  steel  trowel 
for  finishing  because  it  is  believed  to  make  a  more  dense  surface 
which  is  not  slippery.  The  bridge  from  which  the  men  work 
is  a  2  x  12-inch  plank,  trussed  to  prevent  deflection  and  supported 
by  the  side  forms.  No  finishing  should  be  done  while  there  is 
free  water  on  the  surface.  For  finishing  at  unprotected  joints  a 
float  split  lengthwise,  so  as  to  fit  over  the  joint  filler,  is  used. 

1  Owing  to  the  rapid  development  of  belt  finishing  it  is  probable  that  finish- 
ing by  wood  floats  will  not  be  considered  essential  by  many  engineers  after 
this  year. 


CONCRETE   ROADS  103 

Power  finishing  machines  are  now  used  to  some  extent  as  a 
substitute  for  hand  finishing.  They  operate  by  rapidly  increas- 
ing and  decreasing  the  weight  on  the  area  of  concrete  on  which 
they  rest.  These  vibrations  of  load  joggle  the  concrete,  increas- 
ing its  density  and  leaving  a  satisfactory  finish  when  the  con- 
crete has  a  suitable  consistency  and  the  work  is  conducted 
carefully. 

During  1915  and  1916,  an  increasing  use  has  been  made  of 
belt  finishing.  The  work  is  done  with  canvas  belts  from  12  to 
24  inches  wide.  In  Wayne  County,  Michigan,  where  the  method 
has  been  used  for  the  longest  time,  a  12-inch  belt  about  1  foot 
longer  than  the  width  of  the  road,  is  preferred.  It  has  a  handle 
at  each  end  and  is  pulled  gently  back  and  forth  across  the  surface 
after  the  latter  has  been  shaped  by  the  strikeboard.  After  the 
surface  is  finished  in  this  way,  it  is  gone  over  a  second  time  with 
another  belt,  and  sometimes  a  third  time  with  a  third  belt.  The 
belts  are  washed  at  the  close  of  each  day. 

When  belts  are  used  for  finishing  it  is  desirable  to  shape  the 
concrete  with  a  strikeboard  having  a  face  about  8  inches  wide  and 
long  handles  like  those  of  a  plow  at  each  end.  With  such  a  strike- 
board  the  men  can  tamp  as  well  as  shape  the  concrete,  and  thus 
leave  the  surface  in  better  condition  for  the  belt  than  is  the  case 
with  a  thin  strikeboard. 

Curing 

The  protection  and  curing  of  the  concrete  must  be  carried  on 
carefully  because  the  best  concrete  may  be  seriously  damaged 
by  too  rapid  drying  out  of  the  surface  in  hot  or  windy  weather, 
by  exposure  to  low  temperature  or  by  being  opened  to  traffic  too 
soon.  The  principles  which  should  govern  the  work  were  stated 
as  follows  by  the  1916  conference: 

Even  the  best  concrete  may  be  seriously  damaged  by  too  rapid  drying 
out,  early  exposure  to  low  temperature,  or  by  being  opened  to  traffic  at  too 
early  a  period.  Hot  sun  and  drying  winds  are  most  liable  to  dry  out  the 
concrete  too  rapidly,  thus  causing  shrinkage  cracks  or  causing  a  surface 
which  will  not  wear  well  under  traffic.  The  use  of  a  canvas  covering  will 
be  found  effective  in  overcoming  this  condition. 

Sprinkling  should  also  be  employed  as  soon  as  the  concrete  is  hard  enough 
to  prevent  the  surface  being  pitted.  An  earth  covering  or  protection  by 
ponding  should  be  employed  after  the  first  day.  Under  most  favorable 
conditions  such  protection  should  be  given  the  pavement  for  at  least  two 
weeks.  Water  should  be  added  during  this  period  to  keep  the  concrete 
wet. 

In  cool  weather  it  is  often  advisable  to  omit  the  earth  covering,  thus 
allowing  the  concrete  to  harden  more  rapidly.  Sprinkling  should  not  be 
omitted  during  the  day  in  case  the  surface  shows  a  tendency  to  dry  out. 
When  there  is  danger  of  frost,  sprinkling  should  be  omitted  and  a  covering 
of  canvas  or  straw  and  canvas  used. 


104  AMERICAN   HIGHWAY   ASSOCIATION 

Placing  concrete  in  roads  and  pavements  in  temperatures  at  or  near 
freezing  is  not  advisable,  and  if  in  special  cases,  such  work  is  unavoidable, 
the  water  and  aggregate  should  be  heated  and  precautions  taken  to  pro- 
tect the  concrete  from  freezing  for  at  least  ten  days. 

Chemicals  to  lower  the  freezing  temperature  of  the  mixture  should  not 
be  used.  Concrete  should  not  be  deposited  on  a  frozen  subgrade. 

The  canvas  provided  for  protection  during  hot  and  windy 
weather,  should  be  sufficient  to  cover  at  least  half  the  surface 
laid  during  a  day.  Strips  2  yards  wide  are  used  and  they  are 
about  a  yard  longer  than  the  width  of  the  pavement  so  that  each 
end  can  be  weighted.  They  are  supported  on  frames  so  as  not 
to  touch  the  concrete,  and  are  kept  in  place  until  the  concrete 
has  hardened. 

The  curing  of  concrete  by  ponding  is  not  only  more  econom- 
ical in  many  cases  than  the  use  of  wet  earth  but  it  has  a  greater 
advantage  in  permitting  the  inspector  to  determine  at  a  glance 
if  the  curing  is  proceeding  properly.  It  is  difficult  to  make  cer- 
tain that  an  earth  covering  is  kept  properly  wet,  but  there  can 
be  no  question  whether  water  is  standing  on  the  concrete.  Banks 
of  earth  are  constructed  along  each  edge  of  the  pavement  and 
transverse  banks  at  each  expansion  joint  and  more  frequently 
where  the  grades  make  them  necessary.  The  water  is  kept  at 
least  2  inches  deep  over  the  center  of  the  road. 

If  there  is  danger  of  a  heavy  storm  which  will  pit  the  surface 
of  fresh  concrete  it  must  be  protected  by  canvas.  Contractors 
are  advised  to  request  the  nearest  forecasting  station  of  the  United 
States  Weather  Bureau  to  send  its  daily  bulletin  of  the  prob- 
able weather  conditions  during  the  next  thirty-six  hours. 

The  standard  specifications  require  both  water  and  aggre- 
gates to  be  heated  if  the  temperature  drops  to  35  degrees  or  is 
likely  to  do  so  within  twenty-four  hours,  and  the  concrete  laid 
under  these  conditions  must  be  specially  protected  from  freezing 
for  at  least  ten  days.  A  canvas  cover  will  be  sufficient  to  pro- 
tect the  concrete  against  frost  during  the  first  night  and  after 
that  about  3  inches  of  straw  or  marsh  hay  held  down  securely 
will  probably  serve.  If  a  sharp  lowering  of  the  temperature  is 
anticipated  the  straw  should  be  covered  with  canvas.  It  is 
cheaper  to  take  all  necessary  precautions  than  to  tear  out  and 
replace  damaged  concrete.  Even  a  light  freezing  of  the  top 
will  make  the  surface  scale. 

Maintenance 

The  following  explanation  of  methods  of  maintenance  was 
prepared  by  A.  H.  Hinkle,  L.  C.  Herrick,  John  W.  Mueller  and 
Maurice  Hoeffken  for  the  1916  conference: 


CONCRETE   ROADS  105 

Joints  and  cracks  can  be  successfully  treated  by  thoroughly  cleaning 
them  and  filling  when  dry,  and  preferably  during  warm  weather,  with  hot 
tar,  then  covering  with  dry  sand  or  screenings.  The  tar  should  be  per- 
mitted to  lap  over  the  spalled  edges  of  the  crack,  but  not  to  exceed  1  inch. 
The  most  desirable  covering  is  clean,  coarse  sand  or  cleans  creenings  of  stone, 
slag  or  gravel,  that  will  pass  a  $-inch  circular  opening,  and  be  retained 
on  a  ^-inch  mesh  screen.  The  tar  should  be  poured  when  hot  enough  to 
run  readily  into  the  crevices  of  the  pavement  (about  200°  to  250°  F.). 
It  is  believed  that  no  large  excess  of  the  tar  should  be  used  as  the  frequent 
use  of  such  an  excess  might  eventually  build  up  an  elevation  on  the  sur- 
face which  would  be  objectionable  to  traffic.  The  covering  of  screenings 
or  sand  should  be  put  on  immediately  after  pouring  the  tar  so  that  while 
in  the  liquid  state  it  will  unite  with  the  screenings  or  sand  in  sufficient 
degree  to  prevent  the  tar  from  sticking  to  wheels  of  vehicles  or  melting 
during  hot  periods  and  running  from  the  cracks. 

The  use  of  a  mastic  consisting  of  a  mixture  of  hot  tar  and  sand,  in  place 
of  pure  tar,  for  filling  the  cracks  and  joints,  gives  promise  of  excellent 
results;  but  perhaps  it  is  too  soon  to  give  definite  specifications  for  this 
mixture.  The  filling  of  the  larger  and  more  open  cracks  or  joints  with 
the  mastic,  and  the  use  of  the  pure  tar  for  filling  the  minor  openings  in 
the  pavement  and  such  as  are  made  necessary  by  settlement  after  the 
joints  have  been  originally  filled  with  the  mastic,  may  be  found  to  be  most 
satisfactory. 

A  pouring  can  with  a  round  or  vertical  spout  is  very  satisfactory  for 
pouring  tar  in  filling  cracks  and  joints.  Inasmuch  as  it  is  desired  that 
the  tar  shall  lap  over  the  edges  of  the  crack  or  joint,  the  use  of  a  conical 
pouring  can  would  be  of  doubtful  economy. 

Small  holes  and  shallow  depressions  can  be  successfully  treated  as  fol- 
lows: Clean  surface  thoroughly.  Where  the  surface  is  disintegrated  it 
should  first  be  thoroughly  swept  with  a  steel  broom  in  order  to  remove 
all  loose  spalls  or  foreign  matter;  afterward,  the  dust  must  be  removed 
by  sweeping  with  a  rattan  or  house  broom.  The  hot  tar  is  then  applied 
to  the  dry  concrete  and  rubbed  well  with  a  squeegee  or  stiff  broom  to  se- 
cure a  good  bond  to  the  surface  of  the  concrete.  The  tar  is  then  covered 
with  coarse  sand  or  screenings  (^  to  Yg  inch)  of  stone,  slag  or  gravel.  The 
amount  of  tar  used  will  vary  from  \  to  1  gallon  per  square  yard,  depending 
upon  the  depth  of  the  depression  to  be  filled.  When  more  than  \  gallon 
per  square  yard  is  used,  it  should  be  applied  in  two  coats  and  the  excess 
screenings  swept  off  before  the  second  coat  is  applied.  The  more  tar 
that  is  applied  to  the  surface,  the  more  desirable  it  is  to  have  the  coarser 
material  for  a  covering.  In  filling  small  holes  the  application  of  the  tar 
in  two  layers  would,  of  course  be  unnecessary. 

To  repair  larger  holes  and  deeper  depressions  than  those  discussed 
above :  Thoroughly  clean  and  paint  the  surface  with  tar.  Fill  the  hole 
or  depression  with  broken  stone,  preferably  of  such  size  that  they  will 
not  exceed  in  diameter  one-half  the  depth  of  the  depression  to  be  filled 
nor  exceed  in  size  stone  suitable  for  an  ordinary  tar  macadam.  The  stone 
should  be  levelled  off  and  compacted  as  well  as  may  be  by  tamping 
or  rolling  so  as  to  conform  to  the  true  surface  of  the  road.  The  voids  are 
then  filled  with  the  hot  tar  and  screenings  applied  to  the  surface,  which 
is  again  compacted  and  treated  as  in  building  a  tar  macadam. 

The  use  of  a  cold  mix  consisting  of  clean,  hard  stone  chips  coated  with 
a  coal  tar  cutback,  for  filling  such  holes  and  depressions,  as  described 
under  the  above  paragraph,  has  been  followed  to  some  extent  with  very 
promising  results.  The  stone  chips  are  first  thoroughly  coated  with  the 
cold  tar  preparation  by  turning  with  shovels  after  the  tar  has  been 
sprayed  upon  them,  as  in  mixing  ordinary  cement  concrete.  The  mixture  is 


106  AMERICAN   HIGHWAY   ASSOCIATION 

then  permitted  to  stand  a  few  days  until  the  lighter  oils  vaporize  from  the 
tar,  which  leaves  the  stone  coated  with  the  heavy  tar.  The  coated  chips 
are  then  well  tamped  into  the  hole  or  depression  to  be  filled,  the  shallower 
depressions  being  first  painted  with  the  pure  tar.  Coarse  sand  or  fine 
screenings  are  then  spread  over  the  surface.  If  the  voids  appear  quite 
open  after  the  coated  chips  have  been  thoroughly  tamped,  a  light  appli- 
cation of  the  tar  is  made  to  seal  up  the  voids  before  the  surface  screenings 
are  applied. 

Where  the  pavement  is  disintegrated  badly  or  broken  clear  through  so 
as  to  require  rebuilding,  it  should  be  cut  away  with  vertical  edges.  After 
the  subgrade  is  levelled  and  compacted  and  the  edges  and  subgrade  thor- 
oughly dampened  (but  the  foundation  not  made  muddy),  the  part  cut 
away  is  replaced  with  new  concrete  conforming  in  quality  as  nearly  as 
possible  to  the  concrete  of  the  surrounding  pavement.  It  is  well  to  coat 
the  edges  of  the  old  concrete  with  cement  grout.  Care  should  be  taken 
that  the  surface  of  the  new  concrete  conforms  to  the  surface  of  the  adja- 
cent concrete.  The  new  concrete  should  be  kept  well  dampened  for  about 
seven  days,  and  protected  from  traffic  (ten  days  in  warm  weather  and 
much  longer  in  cold  weather)  until  thoroughly  hardened.  If  the  replace- 
ment is  over  an  excavation  the  concrete  should  be  properly  reinforced. 


STANDARD  SPECIFICATIONS  FOR  PORT- 
LAND CEMENT' 

1.  Portland  cement  is  the  product  obtained  by  finely  pul- 
verizing clinker  produced  by  calcining  to  incipient  fusion,  an 
intimate  and  properly  proportioned  mixture  of  argillaceous  and 
calcareous  materials,  with  no  additions  subsequent  to  calcination 
excepting  water  and  calcined  or  uncalcined  gypsum. 

2.  Chemical  Properties. — The    following   limits    shall  not   be 
exceeded: 

Loss  on  ignition,  per  cent 4.00 

Insoluble  residue,  per  cent 0. 85 

Sulfuric  anhydride  (SO3),  per  cent 2.00 

Magnesia  (MgO),  per  cent 5.00 

3.  Physical  Tests. — The  specific  gravity  of  cement  shall  be  not 
less  than  3.10  (3.07  for  white  Portland  cement).     Should  the  test 
of  cement  as  received  fall  below  this  requirement  a  second  test 
may  be  made  upon  an  ignited  sample.    The  specific  gravity  test 
will  not  be  made  unless  specifically  ordered. 

4.  The  residue  on  a  standard  No.  200  sieve  shall  not  exceed  22 
per  cent  by  weight. 

5.  A  pat  of  neat  cement  shall  remain  firm  and  hard,  and  show 
no  signs  of  distortion,  cracking,  checking,  or  disintegration  in 
the  steam  test  for  soundness. 

6.  The  cement  shall  not  develop  initial  set  in  less  than  forty- 
five  minutes  when  the  Vicat  needle  is  used  or  sixty  minutes  when 
the  Gillmore  needle  is  used.    Final  set  shall  be  attained  within 
ten  hours. 

7.  The  average  tensile  strength  in  pounds  per  square  inch  of 
not  less  than  three  standard  mortar  briquettes  composed  of  one 
part  cement  and  three  parts  standard  sand,  by  weight,  shall  be 
equal  to  or  higher  than  the  following: 

1  Adopted  by  the  American  Society  for  Testing  Materials  in  1904  and  re- 
vised in  1908,  1909  and  1916.  These  specifications  are  the  result  of  several 
years'  work  of  a  special  committee  representing  a  United  States  Govern- 
ment Departmental  Committee,  the  Board  of  Direction  of  the  American 
Society  of  Civil  Engineers  and  Committee  C-l  on  Cement  of  the  American 
Society  for  Testing  Materials,  in  cooperation  with  Committee  C-l.  The 
specifications  as  here  printed  are  but  the  first  part  of  the  Society's  "Stand- 
ard Specifications  and  Tests  for  Portland  Cement,"  as  officially  published. 

107 


108  AMERICAN   HIGHWAY   ASSOCIATION 


AGE  AT 

TEST 

STORAGE  07  BRIQUETTES 

TENSILH 
STRENGTH 

day, 

7 

1  day  in  moist  air,  6  days  in  water  

lb.  per  sq.in. 
200 

28 

1  day  in  moist  air,  27  days  in  water  

300 

8.  The  average  tensile  strength  of  standard  mortar  at  twenty  - 
eight  days  shall  be  higher  than  the  strength  at  seven  days. 

9.  Packages,  Marking  and  Storage. — The  cement  shall  be  de- 
livered in  suitable  bags  or  barrels  with  the  brand  and  name  of 
the  manufacturer  plainly  marked  thereon,  unless  shipped  in 
bulk.     A  bag  shall  contain  94  pounds  net.     A  barrel  shall  con- 
tain 376  pounds  net. 

10.  The  cement  shall  be  stored  in  such  a  manner  as  to  permit 
easy  access  for  proper  inspection  and  identification  of  each  ship- 
ment, and  in  a  suitable  weather-tight  building  which  will  protect 
the  cement  from  dampness. 

11.  Inspection. — Every  facility  shall  be  provided  the  purchaser 
for  careful  sampling  and  inspection  at  either  the  mill  or  at  the 
site  of  the  work,  as  may  be  specified  by  the  purchaser.     At  least 
ten  days  from  the  time  of  sampling  shall  be  allowed  for  the  com- 
pletion of  the  7-day  test,  and  at  least  31  days  shall  be  allowed  for 
the  completion  of  the  28-day  test.    The  cement  shall  be  tested 
in  accordance  with  the  methods  hereinafter  prescribed.     The 
28-day  test  shall  be  waived  only  when  specifically  ordered. 

12.  Rejection. — The  cement  may  be  rejected  if  it  fails  to  meet 
any  of  the  requirements  of  these  specifications. 

13.  Cement  shall  not  be  rejected  on  account  of  failure  to  meet 
the  fineness  requirement  if  upon  retest  after  drying  at  100°C. 
for  one  hour  it  meets  this  requirement. 

14.  Cement  failing  to  meet  the  test  for  soundness  in  steam 
may  be  accepted  if  it  passes  a  retest  using  a  new  sample  at  any 
time  within  28  days  thereafter. 

15.  Packages  varying  more  than  5  per  cent  from  the  specified 
weight  may  be  rejected;  and  if  the  average  weight  of  packages 
in  any  shipment,  as  shown  by  weighing  50  packages  taken  at 
random,  is  less  than  that  specified,  the  entire  shipment  may  be 
rejected. 


PETROLEUM  AND  RESIDUUMS* 

A  large  part  of  the  materials  used  as  dust  preventives  and 
binders  to  hold  together  the  mineral  constituents  of  roads  are 
obtained  from  petroleum.  Petroleum  is  a  term  which  covers 
mineral  oils  of  a  great  variety  of  characteristics,  all  alike  in  being 
composed  of  a  great  variety  of  complex  chemical  compounds 
called  hydrocarbons,  of  which  there  is  a  very  large  number. 
The  investigation  of  the  properties  of  these  hydrocarbons  and 
their  derivatives  requires  a  knowledge  of  organic  chemistry  which 
few  roadbuilders  possess,  and  because  some  of  them  have  at- 
tempted to  tread  the  veritable  mazes  of  this  extremely  compli- 
cated domain  of  chemistry,  no  little  confusion  has  arisen.  The 
main  facts  regarding  petroleum  and  the  other  hydrocarbons  used 
in  roadbuilding  are  definitely  known,  but  the  details  of  any  group 
of  these  compounds  are  best  left  for  the  chemical  specialist,  who 
is  making  steady  progress  in  his  researches  concerning  them. 

Paraffin  and  Asphaltic  Oils 

The  roadbuilder's  interest  in  petroleum  is  largely  in  its  base, 
a  term  used  to  designate  a  part  of  oil  left  after  distilling  off  the 
more  volatile  portions.  The  base  is  sometimes  made  up  of  com- 
pounds of  the  paraffin  group  or  series,  as  chemists  term  such 
allied  compounds.  Marsh  gas  is  a  member  of  the  paraffin  series, 
and  its  least  complex  representative.  A  few  other  members  are 
gases  but  most  of  them  are  liquids  or  solids,  and  their  number  is 
legion.  The  base  of  other  petroleums  is  made  up  of  compounds 
called  polycyclic  polymethylenes  by  the  chemist,  and  as  these 
compounds  occur  in  native  asphalts  such  a  base  is  called  asphaltic. 
The  base  of  other  petroleums  is  made  up  of  both  paraffin  and 
asphaltic  compounds  and  such  petroleums  are  called  semi- 
asphaltic. 

The  gaseous  hydrocarbons  are  of  no  interest  to  the  roadbuilder. 
The  liquid  and  solid  hydrocarbons  are  what  determine  the  value 
of  petroleum  for  his  purposes.  The  liquid  and  solid  paraffins  are 
greasy  materials  without  binding  properties,  while  the  asphaltic 
materials  are  sticky.  Consequently  the  roadbuilding  value  of 
petroleum  depends  upon  the  asphaltic  compounds  in  its  base. 

1  Revised  by  PreVost  Hubbard,  chief  of  road  materials  tests  and  re- 
search, United  States  Office  of  Public  Roads. 

109 


110  AMERICAN  HIGHWAY  ASSOCIATION 

Paraffin  oils  have  been  used  successfully  as  dust  preventives 
when  sprinkled  in  small  quantities  on  a  clean  road,  but  if  used  in 
large  quantities  they  form  a  greasy,  dirty  surface  and  seem  to 
lubricate  the  pieces  of  stone  in  the  road,  which  becomes  rutted 
rapidly. 

Petroleum  is  obtained  from  many  districts,  which  are  called 
fields  in  the  industry.  The  leading  fields  which  supply  or  have 
supplied  materials  for  roadbuilding  in  the  United  States  are 
discribed  substantially  as  follows  by  John  D.  Northrop  in  Mineral 
Resources  of  the  United  States,  1915: 

1.  The  Appalachian  field  embraces  all  oil  pools  east  of  central 
Ohio  and  north  of  central  Alabama,  including  those  of  New  York, 
Pennsylvania,    West    Virginia,    southeastern    Ohio,    Kentucky, 
Tennessee,  and  northern  Alabama.    The  oils  of  the  Appalachian 
field  are  in  the  main  of  paraffin  base,  free  from  asphalt  and  prac- 
tically free  from  sulphur,  and  they  yield  by  ordinary  refining 
methods  high  percentages  of  gasoline  and  illuminating  oils — the 
products  in  greatest  demand. 

2.  The  Lima-Indiana  field  embraces  all  areas  of  oil  production 
in  the  northwestern  part  of  Ohio  and  in  Indiana.    The  petroleum 
of  the  Lima-Indiana  field  contains  some  asphalt,  though  con- 
sisting chiefly  of  paraffin  hydrocarbons  with  sulphur  compounds. 

3.  The  Illinois  field  lies  in  the  southeastern,  south-central  and 
western  parts  of  the  State,  comprising  about  16  counties.    Illinois 
oils  contain  varying  proportions  of  both  asphalt  and  paraffin 
and  differ  considerably  as  to  specific  gravity  and  distillation 
products.    Sulphur  is  generally  present. 

For  commercial  purposes  it  is  customary  to  group  under  the 
title  "Mid-Continent  field"  the  areas  of  oil  production  in  Kansas, 
Oklahoma,  northern  and  central  Texas,  and  northern  Louisiana. 
Mid-continent  oils  vary  in  composition  within  wide  limits,  rang- 
ing from  asphaltic  oils  poor  in  gasoline  and  illuminants,  to  oils 
in  which  the  asphalt  content  is  negligible  and  the  paraffin  con- 
tent relatively  high  and  which  yield  correspondingly  high  per- 
centages of  the  lighter  products  on  distillation.  Sulphur  is  pres- 
ent in  varying  quantities  in  the  lower  grade  oils. 

5.  The  term  "Gulf  field"  includes  that  portion  of  the  gulf 
coastal  plain  of  Texas  and  Louisiana  in  which  petroleum  is  found 
in  domes,  associated  with  rock  salt  and  gypsum.     Oils  from  the 
Gulf  field  are  characterized  by  relatively  high  percentages  of 
asphalt  and  low  percentages  of  the  lighter  gravity  distillation 
products.     Considerable  sulphur  is  present,  much  of  which,  how- 
ever, is  in  the  form  of  sulphureted  hydrogen  and  is  easily  removed 
by  steam  before  refining  or  utilizing  the  oil  as  fuel. 

6.  The  California  field  is  mainly  located  in   Kern,   Fresno, 
Orange,  Santa  Barbara  and  Los  Angeles  Counties.    The  Cali- 


PETROLEUM   AND   RESIDUUMS 


111 


fornia  oils  are  generally  characterized  by  much  asphalt  and  little 
or  no  paraffin  and  by  small  proportions  of  sulphur.  The  chief 
products  are  fuel  oils,  lamp  oils,  lubricants,  and  oil  asphalt. 

Oils  from  Wyoming  and  Colorado  are  in  the  main  of  paraffin 
base,  suitable  for  refining  by  ordinary  methods.  Heavy  asphaltic 
oils  are  also  obtained  in  certain  of  the  Wyoming  fields. 

7.  Mexican  field.     This  extends  along  the  Gulf  of  Mexico  from 
the  vicinity  of  Tampico  to  the  vicinity  of  Tuxpan,  and  produces 
asphaltic  and  semi-asphaltic  petroleum. 

8.  Trinidad  field.     A  large  amount  of  asphaltic  petroleum  is 
produced  on  the  island  of  Trinidad. 

Clifford  Richardson  gives  the  following  explanation  of  the  rela- 
tion between  this  petroleum  and  Trinidad  asphalt: 

Rising  from  the  sands  in  which  it  occurs  and  coming  in  contact  with  the 
colloidal  clay  forming  a  portion  of  the  mud  existing  below  the  crater  or 
depression  which  holds  the  asphalt,  it  is  emulsified  with  it  and  converted 
into  the  material  which  we  recognize  as  Trinidad  lake  asphalt. 

Refining  Petroleum 

Crude  asphaltic  petroleum  has  been  used  as  a  dust  preventive 
and  as  a  binder,  but  generally  the  petroleum  is  refined  to  obtain 
a  number  of  valuable  materials  occurring  in  it.  The  crude  oil 
is  first  allowed  to  settle  in  tanks  in  which  the  mineral  matter 

Petroleum  Marketed  in  the  United  States  in  1915  by  Fields 
(John  D.  Northrop,  in  Mineral  Resources  of  the  United  States,  1915) 


FIELD. 

QUANTITY  (BAR- 
EELS  OF  42  GAL- 
LONS) 

VALUE 

AVERAGE  PRIOB 
PER  BARREL 

Appalachian  

22,860,048 

$35  468,973 

$1  552 

Lima-Indiana 

4  269  591 

4  114  228 

0  964 

Illinois 

19  041  695 

18  655  850 

0  980 

Mid-continent 

123  295  867 

72  437  701 

0  588 

Gulf 

20  577  103 

9  802  901 

0  476 

California..   . 

86  591  535 

36  558  439 

0  422 

Colorado  and  Wyoming 

4  454  000 

2  400  503 

0  539 

Other  fields  

14  265* 

24  295* 

1  703 

281,104,104 

$179,462,890 

$0.638 

*  Includes  Alaska,  Michigan,  and  Missouri. 

NOTE  :  The  Barber  Asphalt  Company  reports  that  the  importation  of 
crude  petroleum  from  Trinidad  has  been  as  follows:  1914,  140,438  barrels; 
1915,  330,022  barrels;  1916,  372, uOO  barrels.  The  imports  of  crude  petro- 
leum from  Mexico  are  reported  by  John  D.  Northrop  as  follows:  1914, 
16,245,975;  1915,  17,478,472  barrels. 

A  preliminary  estimate  by  J.  D.  Northrop  of  the  1916  production  in  the 
United  States  is  292,300,000  barrels. 


112 


AMERICAN   HIGHWAY   ASSOCIATION 


Degrees  Baume,  Specific  Gravities,  Weights  in  Pounds  per  Gallon  and  Volume 

in  Gallons  per  Pound  of  Petroleum  at  60°F. 

(From  "United  States  Standard  Tables  for  Petroleum  Oils,"  United  States 
Bureau  of  Standards) 


D  EGREE8 
BAUMri 

SPECIFIC 
GRAVITY 

POUNDS  PER 
GALLON 

GALLONS 
PER  POUND 

DEGREES 

BAUM£ 

SPECIFIC 
GRAVITY 

POUNDS  PER 
GALLON 

GALLONS 
PER  POUND 

10.0 

1.0000 

8.328 

0.1201 

19.6 

0.9358 

7.793 

0.1283 

10.2 

0.9986 

8.317 

0.1202 

19.8 

0.9346 

7.783 

0.1285 

10.4 

0.9972 

8.305 

0.1204 

20.0 

0.9333 

7.772 

0.1287 

10.6 

0.9957 

8.293 

0.1206 

20.2 

0.9321 

7.762 

0.1288 

10.8 

0.9943 

8.281 

0.1208 

20.4 

0.9309 

7.752 

0.1290 

11.0 

0.9929 

8.269 

0.1209 

20.6 

0.9296 

7.742 

0.1292 

11.2 

0.9915 

8.258 

0.1211 

20.8 

0.9284 

7.731 

0.1293 

11.4 

0.9901 

8.246 

0.1213 

21.0 

0.9272 

7.721 

0.1295 

11.6 

0.9887 

8.234 

0.1214 

21.2 

0.9259 

7.711 

0.1297 

11.8 

0.9873 

8.223 

0.1216 

21.4 

0.9247 

7.701 

0.1299 

12.0 

0.9859 

8.211 

0.1218 

21.6 

0.9235 

7.690 

0.1300 

12.2 

0.9845 

8.199 

0.1220 

21.8 

0.9223 

7.680 

0.1302 

12.4 

0.9831 

8.188 

0.1221 

22.0 

0.9211 

7.670 

0.1304 

12.6 

0.9818 

8.176 

0.1223 

22.2 

0.9198 

7.660 

0.1305 

12.8 

0.9804 

8.165 

0.1225 

22.4 

0.9186 

7.650 

0.1307 

13.0 

0.9790 

8.153 

0.1227 

22.6 

0.9174 

7.640 

0.1309 

13.2 

0.9777 

8.142 

0.1228 

22.8 

0.9162 

7.630 

0.1311 

13.4 

0.9763 

8.131 

0.1230 

23.0 

0.9150 

7.620 

0.1313 

13.6 

0.9749 

8.119 

0.1232 

23.2 

0.9138 

7.610 

0.1314 

13.8 

0.9736 

8.108 

0.1233 

23.4 

0.9126 

7.600 

0.1316 

14.0 

0.9722 

8.096 

0.1235 

23.6 

0.9115 

7.590 

0.1318 

14.2 

0.9709 

8.086 

0.1237 

23.8 

0.9103 

7.580 

0.1319 

14.4 

0.9695 

8.074 

0.1239 

24.0 

0.9091 

7.570 

0.1321 

14.6 

0.9682 

8.063 

0.1240 

24.2 

0.9079 

7.561 

0.1323 

14.8 

0.9669 

8.052 

0.1242 

24.4 

0.9067 

7.551 

0.1324 

15.0 

0.9655 

8.041 

0.1244 

24.6 

0.9056 

7.541 

0.1326 

15.2 

0.9642 

8.030 

0.1245 

24.8 

0.9044 

7.531 

0.1328 

15.4 

0.9629 

8.019 

0.1247 

25.0 

0.9032 

7.522 

0.1330 

15.6 

0.9615 

8.007 

0.1249 

25.2 

0.9021 

7.512 

0.1331 

15.8 

0.9602 

7.997 

0.1250 

25.4 

0.9009 

7.502 

0.1333 

16.0 

0.9589 

7.986 

0.1252 

25.6 

0.8997 

7.493 

0.1335 

16.2 

0.9576 

7.975 

0.1254 

25.8 

0.8986 

7.483 

0.1336 

16.4 

0.9563 

7.964 

0.1256 

26.0 

0.8974 

7.473 

0.1338 

16.6 

0.9550 

7.953 

0.1257 

26.2 

0.8963 

7.464 

0.1340 

16.8 

0.9537 

7.942 

0.1259 

26.4 

0.8951 

7.454 

0.1342 

17.0 

0.9524 

7.931 

0.1261 

26.6 

0.8940 

7.445 

0.1343 

17.2 

0.9511 

7.921 

0.1262 

26.8 

0.8929 

7.435 

0.1345 

17.4 

0.9498 

7.910 

0.1264 

27.0 

0.8917 

7.425 

0.1347 

17.6 

0.9485 

7.899 

0.1266 

27.2 

0.8906 

7.416 

0.1348 

17.8 

0.9472 

7.888 

0.1268 

27.4 

0.8895 

7.407 

0.1350 

18.0 

0.9459 

7.877 

0.1270 

27.6 

0.8883 

7.397 

0.1352 

18.2 

0.9447 

7.867 

0.1271 

27.8 

0.8872 

7.388 

0.1354 

18.4 

0.9434 

7.856 

0.1273 

28.0 

0.8861 

7.378 

0.1355 

'  18.6 

0.9421 

7.846 

0.1275 

28.2 

0.8850 

7.369 

0.1357 

18.8 

0.9409 

7.835 

0.1276 

28.4 

0.8838 

7.360 

0.1359 

19.0 

0.9396 

7.825 

0.1278 

28.6 

0.8827 

7.351 

0.1360 

19.2 

0.9383 

7.814 

0.1280 

28.8 

0.8816 

7.341 

0.1362 

19.4 

0.9371 

7.804 

0.1281 

29.0 

0.8805 

7.332 

0.1364 

NOTE:  Tables  for  oils  of  greater  specific  gravity  than  1.000  and  of  the 
comparative  volumes  of  oils  at  60°  and  other  temperatures  are  given  on 
pages  129  and  131. 


PETEOLEUM   AND   RESIDUUM8  113 

and  water  are  separated  from  the  oil.  The  latter  is  drawn  off 
into  cylindrical  stills  set  horizontally  in  brickwork  like  boilers. 
There  is  a  furnace  below  the  still,  and  the  latter  contains  steam 
coils  and  sometimes  steam  jets  at  the  bottom  of  the  stills.  The 
heating  by  means  of  the  furnace  and  the  steam  coils  and  jets 
should  be  conducted  very  carefully,  if  the  final  products  are  to 
be  used  for  road  work,  and  careless  heating  has  resulted  in  very 
undesirable  materials  being  sold  for  highway  purposes.  The 
vapors  from  the  stills  are  removed  to  condensers  and  liquefied. 

The  distillate  that  is  obtained  until  the  temperature  reaches 
about  300°F.  and  the  specific  gravity  of  the  product  is  about  0.73 
is  refined  to  furnish  gasoline  and  naphtha.  While  the  tempera- 
ture is  increased  from  300°  to  575°F.,  the  specific  gravity  of  the 
distillate  increases  to  about  0.82,  and  the  oil  produced  during 
this  stage  is  treated  to  supply  kerosene.  If  it  is  desirable  to  pro- 
duce as  much  kerosene  as  possible  the  furnace  is  heated  and  the 
sides  of  the  still  kept  as  cool  as  possible,  so  that  some  of  the 
heavy  vapor  driven  off  in  the  bottom  of  the  still  will  condense 
in  the  top  and  fall  back  into  the  much  hotter  material  at  the 
bottom,  "cracking"  these  heavy  vapors  into  lighter  compounds. 
One  result  of  such  cracking  is  often  the  liberation  of  free  carbon, 
which  settles  into  the  material  in  the  bottom  of  the  still.  As- 
phaltic oils  can  be  cracked  at  a  lower  temperature  than  paraffin 
oils. 

If  road  oils  for  surface  treatment  are  desired,  the  distilling 
process  is  stopped  after  the  light  distillates  are  driven  off.  The 
thick  oil  left  in  the  still  is  called  the  residuum,  and  some  people 
look  upon  it  as  a  by-product  and  the  name  "residuum"  as  having 
a  somewhat  derogatory  signification.  As  a  matter  of  fact  the 
residuum  obtained  in  distilling  some  petroleums  is  by  far  the  most 
important  product  obtained  from  them.  Some  Calif ornian  and 
Mexican  oils  contain  such  a  large  amount  of  asphaltic  compounds 
and  so  little  light  oils  that  by  stopping  the  refining  process  when 
the  residuum  has  the  consistency  desired  for  some  classes  of 
paving  materials,  it  is  unnecessary  to  add  any  other  bitumen  to 
fit  it  for  use. 

In  the  patented  Trumbull  process,  the  oil  is  heated  and  then 
allowed  to  flow  down  the  inner  surface  of  a  large  vertical  heated 
cylinder.  The  vapors  are  drawn  from  the  top  of  the  cylinder 
and  the  asphaltic  residuum  is  collected  at  the  bottom.  The 
temperatures  used  and  the  rate  at  which  the  crude  oil  is  fed  to 
the  top  of  the  cylinder  fix  the  consistency  of  the  residuum. 

One  of  the  earliest  attempts  to  improve  the  process  of  refining 
petroleum  so  as  to  yield  the  maximum  quantity  of  products  useful 
for  paving  was  made  by  Dubbs.  By  adding  sulphur  to  the 
residuum  while  it  was  at  a  high  temperature  he  produced  mate- 


114  AMERICAN  HIGHWAY  ASSOCIATION 

rials  which  have  been  widely  used  as  fluxes.  About  the  same 
time  Byerly  found  that  by  blowing  air  through  the  heated  re- 
siduum asphaltic  products  were  obtained,  the  oxygen  performing 
the  same  function  as  the  sulphur  used  in  the  Dubbs  process. 
Some  of  these  blown-oil  products  have  been  used  as  fluxes  and 
others  have  been  used  for  a  great  variety  of  purposes.  Some 
asphaltic  oils  furnish  a  residuum  which  does  not  require  blowing 
to  obtain  road  material  but  this  treatment  is  generally  employed 
with  semi-asphaltic  oils  when  such  a  product  is  desired.  Appar- 
ently the  hydrocarbons  of  the  paraffin  series  are  little  affected  by 
the  blowing  process,  which  affects  compounds  of  other  series. 

Meaning  of  Analyses. — The  characteristics  of  the  residuums 
from  various  oils  are  given  in  the  accompanying  table.  The  fol- 
lowing notes  explain  the  significance  of  the  information  in  the 
table,  and  are  abridged  from  Pr&vost  Hubbard's  Dust  Preventives 
and  Road  Binders. 

Specific  Gravity.— The  mark  "25°/25°C."  indicates  that  the 
determination  was  made  at  25°C.  (77°F.)  and  the  result  expressed 
in  comparison  with  water  at  the  same  temperature.  The  test 
is  mainly  useful  in  identifying  the  material,  but  also  gives  a  rough 
indication  of  the  amount  of  heavy  hydrocarbons  which  give 
body  to  the  material.  Material  having  a  specific  gravity  exceed- 
ing 0.93  or  0.94  should  be  heated  before  use. 

Flash  Point. — This  test  is  of  value  as  differentiating  between 
the  heavy  crude  oils  and  cut-back1  products,  and  the  fluid  re- 
siduums. It  also  shows  the  point  to  which  a  refined  oil  has  been 
distilled  and  whether  it  is  advisable  to  heat  the  material  before 
application. 

Loss  at  160°C. — The  loss  in  weight  is  an  indication  of  the  rela- 
tive losses  by  volatilization  of  different  road  oils  in  actual  service. 
It  is  an  empirical  test,  like  the  rattler  test  for  paving  bricks.  The 
residue  should  be  sticky.  If  it  is  desirable  for  the  material  to 
maintain  its  consistency  after  application,  it  should  show  a  low 
loss.  If  the  material  is  applied  by  a  method  which  requires  more 
or  less  fluidity,  a  high  loss  is  permissible,  in  order  that  the  mate- 
rial may  rapidly  attain  the  desired  consistency  in  the  road, 
although  a  high  loss  is  not  necessary  in  the  case  of  dust  preven- 
tives. The  loss  is  now  usually  determined  at  163°C. 

Loss  at  205°C. — The  purpose  of  this  test  is  to  show  the  effect 
of  a  high  temperature  as  compared  with  160°  or  163°.  It  is  not 
often  made. 

Bitumen  Soluble  in  082. — The  solubility  of  the  bitumen  itself 
is  independent  of  its  character  and  consistency,  so  the  amount 
and  character  of  insoluble  material  is  of  most  interest. 

1  A  cut-back  product  is  one  made  by  fluxing  a  dense  asphalt  with  a 
light  oil. 


PETROLEUM  AND  RESIDUUMS 


115 


116  AMERICAN  HIGHWAY  ASSOCIATION 

Inorganic  Matter. — This  indicates  in  some  cases  the  nature  of 
the  dense  bitumen. 

Insoluble  Organic  Matter. — This  affords  an  indication  of 
whether  oil  has  been  distilled  destructively. 

Bitumen  Insoluble  in  88°B.  Naphtha. — The  hydrocarbons  in- 
soluble in  paraffin  naphtha  are  termed  "asphaltenes"  and  those 
which  are  soluble  "malthenes."  The  former  tend  to  give  body 
and  consistency  and  the  latter  contribute  adhesive  properties  to 
a  road  material.  Blown  oils  contain  very  high  amounts  of  insol- 
uble hydrocarbons,  sometimes  as  much  as  25  to  30  per  cent.  The 
character  of  the  bitumen  dissolved  in  naphtha,  after  the  solvent 
has  evaporated,  is  instructive,  for  a  sticky  residue  indicates  better 
road  building  qualities  in  the  original  material  than  that  which 
is  greasy. 

Soluble  Bitumen  Removed  by  H2S04  and  Saturated  Hydro- 
carbons in  Total  Bitumen. — These  tests  are  mainly  of  value  as 
indicating  the  source  of  the  material  under  examination.  Clifford 
Richardson  gives  the  following  explanation  of  the  significance  of 
the  tests  in  The  Modem  Asphalt  Pavement: 

Hydrocarbons  in  general  are  divided  into  those  which  are  saturated 
and  those  which  are  unsaturated,  the  former  being  stable  and  the  latter 
reactive  and  very  susceptible  to  change,  combining  with  or  being  con- 
verted into  other  hydrocarbons  by  the  action  of  sulphuric  acid  and  other 
reagents.  The  saturated  can  be  separated  from  the  unsaturated  hydro- 
carbons by  strong  sulphuric  acid,  and  this  will  be  found  to  be  a  very  impor- 
tant means  of  differentiating  the  oils  and  the  solid  bitumens  among  them- 
selves, by  determining  the  relative  proportions  of  these  two  classes  of 
hydrocarbons  which  they  contain. 

Solid  Paraffin. — This  test  confirms  the  information  obtained 
from  an  inspection  of  the  residue  after  the  test  of  the  loss  at 
160°C.  The  heavy  liquid  hydrocarbons  of  the  paraffin  series  are 
probably  more  detrimental  in  road  oils  than  are  the  solid  paraffins. 

Fixed  Carbon. — Fixed  carbon  is  the  coke  resulting  from  the 
ignition  of  the  bitumen  in  the  absence  of  oxygen. 

Fluxes 

Fluxes  are  petroleum  products  which  are  mixed  with  harder 
bituminous  materials  to  soften  them  to  any  desired  consistency. 
Petroleum  with  a  paraffin  base  furnished  the  first  flux  used  in 
the  asphalt  paving  industry. 

Asphaltic  or  semi-asphaltic  flux  is  the  residuum  left  on  distilling 
petroleum  having  an  asphaltic  or  semi-asphaltic  base  to  a  point 
where  the  residuum  is  a  dense  liquid  when  cool  but  any  further 
distillation  will  produce  a  solid  residuum  when  cold.  It  is  char- 
acterized by  a  relatively  low  amount  of  saturated  hydrocarbons. 
While  it  resembles  natural  maltha  in  some  respects,  it  differs  in 
remaining  soft  after  heating  to  400°F.,  most  malthas  becoming 
hard  pitches  after  such  treatment. 


ASPHALT  AND  NATIVE  SOLID  BITUMENS' 

The  following  definition  of  "asphalt"  has  been  adopted  by  the 
American  Society  for  Testing  Materials: 

Solid  or  semi-solid  native  bitumens,  solid  or  semi-solid'  bitumens 
obtained  by  refining  petroleum,  or  solid  or  semi-solid  bitumens  which  are 
combinations  of  the  bitumens  mentioned  with  petroleums  or  derivatives 
thereof,  which  melt  upon  the  application  of  heat  and  which  consist  of  a 
mixture  of  hydrocarbons  and  their  derivatives  of  complex  structure, 
largely  cyclic  and  bridge  compounds. 

This  definition  is  dependent  upon  the  same  society's  definition 
of  "bitumens,"  which  is: 

Mixtures  of  native  or  pyrogenous  hydrocarbons  and  their  non-metallic 
derivatives,  which  may  be  gases,  liquids,  viscous  liquids,  or  solids,  and 
which  are  soluble  in  carbon  disulphide. 

These  definitions  were  prepared  after  numerous  conferences  of 
road  engineers  and  producers  of  materials,  and  while  adopted  by 
the  society  are  not  accepted  by  all  specialists. 

The  following  definitions  are  given  by  Clifford  Richardson  in 
The  Modern  Asphalt  Pavement: 

Native  bitumens  consist  of  a  mixture  of  native  hydrocarbons  and  their 
derivatives,  which  may  be  gaseous,  liquid,  a  viscous  liquid  or  solid,  but, 
if  solid,  melting  more  or  less  readily  on  the  application  of  heat,  and  solu- 
ble in  turpentine,  chloroform,  bisulphide  of  carbon,  similar  solvents,  and 
in  the  malthas  or  heavy  asphaltic  oils.  Natural  gas,  petroleum,  maltha, 
asphalt,  grahamite,  gilsonite,  ozocerite,  etc.,  are  bitumens.  Coal,  lignite, 
wurtzelite,  albertite,  so-called  indurated  asphalts,  are  not  bitumens,  be- 
cause they  are  not  soluble  to  any  extent  in  the  u^ual  solvents  for  bitumen, 
nor  do  they  melt  at  comparatively  low  temperatures  nor  dissolve  in  heavy 
asphaltic  oils.  These  substances,  however,  on  destructive  distillation 

1  Revised  by  Provost  Hubbard,  chief  of  road  materials  tests  and  re- 
search, United  States  Office  of  Public  Roads. 

2  Solid  bituminous  materials  are  those  having  a  penetration  at  25°C. 
(77°F.)  under  a  load  of  100  grams  applied  for  five  seconds,  of  not  more  than 
10.    The  significance  of  "  penetration"  is  explained  on  page  121. 

Semi-solid  bituminous  materials  are  those  having  a  penetration  at  25°C. 
(77°  F.)  under  a  load  of  100  grams  applied  for  five  seconds,  of  more  than 
10  and  a  penetration  under  a  load  of  50  grams  applied  for  1  second  of  not 
more  than  350. 

Liquid  bituminous  materials  are  those  having  a  penetration  at  25°C. 
(77°  F).)  under  a  load  of  50  grams  applied  for  one  second  or  more  than 
350.. 

117 


118  AMERICAN  HIGHWAY  ASSOCIATION 

give  rise  to  products  which  are  similar  to  natural  bitumens,  and  they  have 
been  on  this  account  defined  by  T.  Sterry  Hunt  as  "pyro-bitumens," 
which  differentiates  them  very  plainly  from  the  true  bitumens." 

Asphalt  is  a  term  used  industrially  to  cover  all  the  solid  native  bitu- 
mens used  in  the  paying  industry  and  specifically  to  include  only  such  as 
melt  on  the  application  of  heat,  at  about  the  temperature  of  boiling  water, 
are  equally  soluble  in  carbon  bisulphide  and  carbon  tetrachloride  and  to 
a  large  extent  in  88°  naphtha,  those  hydrocarbons  soluble  in  naphtha 
consisting  to  a  very  considerable  degree  of  saturated  hydrocarbons,  yield- 
ing about  15  per  cent  of  fixed  carbon  and  containing  a  high  percentage  of 
sulphur.  Under  this  definition  it  can  be  seen  that  grahamite  is  not  an 
asphalt,  since  it  is  not  largely  soluble  in  naphtha  and  yields  a  very  high 
percentage  of  fixed  carbon  on  ignition.  It  is  also  less  soluble  in  carbon 
tetrachloride  than  in  carbon  bisulphide.  Gilsonite  is  not  an  asphalt, 
since  the  saturated  hydrocarbons  contained  in  the  naphtha  solution  are 
very  small  in  amount  and  quite  different  in  character  from  those  found 
in  asphalt. 

Roadbuilders  use  the  term  "natural  asphalts"  to  designate 
the  native  solid  or  semi-solid  asphalts,  and  "oil  asphalts"  to  desig- 
nate the  corresponding  materials  prepared  from  petroleum  or 
maltha.  Some  producers  of  oil  asphalts  object  to  the  term  on 
the  ground  that  the  material  obtained  by  distilling  away  the 
lighter  parts  of  asphaltic  petroleum  is  as  "natural"  as  that 
obtained  by  refining  native  asphalts.  By  "rock  asphalt"  is 
meant  sandstone  and  limestone  impregnated  with  asphalt  or 
maltha.  "Asphaltic  sands"  are  mixtures  of  asphalt  or  maltha 
and  sand,  the  latter  in  loose  grains  which  fall  apart  when  the 
bitumen  is  extracted;  many  of  them  are  called  rock  asphalts 
because  in  their  natural  condition  the  maltha  cements  them  into 
a  rock-like  mass. 

The  sources  of  the  asphalts  used  in  the  United  States  are  given 
in  the  accompanying  table.  The  quantities  of  materials  there 
stated  were  not  all  used  for  road  and  street  purposes,  as  there  are 
many  other  uses  to  which  some  of  them  are  put. 

Trinidad  Asphalt. — Trinidad  asphalt  comes  from  the  island  of 
that  name.  The  main  source  is  on  La  Brea  Point,  about  28  miles 
from  Port  of  Spain,  the  chief  town.  Here  there  is  a  circular  pitch 
lake  of  nearly  115  acres  extent,  between  which  and  the  sea  are 
other  pitch  deposits  more  or  less  mixed  with  sand.  The  former 
furnishes  the  "lake  asphalt"  and  the  latter  the  "land  asphalt" 
of  the  paving  industry. 

The  material  in  the  lake  is  described  by  Clifford  Richardson 
as  an  emulsion  of  water,  gas,  bitumen,  fine  sand  and  clay.  It  is 
in  constant  motion  owing  to  the  evolution  of  gas,  and  for  this 
reason,  whenever  a  hole  is  dug  in  the  surface,  whether  deep  or 
shallow,  it  rapidly  fills  up  and  the  surface  resumes  its  original 
level  after  a  short  time.  Although  soft  it  can  be  readily  flaked 
out  with  picks  in  large  conchoidal  masses  weighing  50  to  75 


ASPHALT  AND   NATIVE   SOLID   BITUMENS 


119 


pounds.  It  is  honey-combed  with  gas  cavities  and  resembles  a 
Swiss  cheese  in  structure.  It  is  of  uniform  composition,  as 
follows:  Water  and  gas  volatilized  at  100°C.,  29  per  cent;  bitumen 
soluble  in  cold  carbon  disulphide,  39  per  cent;  bitumen  absorbed 

American  Production  and  Importation  of  Asphaltic  Materials,  1915 

(Compiled  from  report  by  John  D.  Northrop  in  Mineral  Resources  of  the 

United  States,  1915.    Output  stated  in  tons  of  2000  pounds,  except 

in  case  of  imports,  which  are  in  tons  of  2240  pounds) 


19 

15 

19 

14 

Tons 

Value 

Tons 

Value 

American  bituminous  rock  .... 
Wurtzelite  (elaterite),  gilsonite 
Grahamite  

44,329 
20,559 
10,863 

$157,083 
275,252 
94,155 

51,071 

19,148 
9,669 

$162,622 
405,966 
73,535 

Total  American  natural  bitu- 
minous material 

75751 

526  490 

79  888 

642  123 

American  road  oils  and  fluxes. 

417,859 

2,392,576 

171,447 

American    oil    asphalts    and 
pitches  

246,644 

2,323,007 

189,408 

Total  American  road  oils,  as- 
phalts, etc. 

664,503 

4,715,583 

360,855f 

3,016,969 

Mexican  road  oils  and  fluxes* 

174,854 

1,325,201 

111,058 

Mexican     oil     asphalts     and 
pitches*  

213,464 

2,405,235 

202,729 

Total  Mexican  road  oils,  as- 
phalts, etc* 

388,318 

3,730,436 

313  787 

4  131,153 

Imports  of  asphalt 
Trinidadf  .. 

92,107 

498,900 

61,708 

334,635 

Bermudez  

28,659 

144,595 

58,755 

295,765 

Cuba  

391 

9,243 

458 

11,407 

Barbados  

64 

6,426 

71 

6,592 

Mexico  

56 

755 

140 

2,048 

Switzerland 

200 

1  637 

620 

3  706 

Italy 

492 

3,438 

247 

1  477 

France 

100 

1,317 

England  ...               .    . 

774 

9,801 

628 

6,269 

Germany  ... 

658 

4,854 

1,354 

10,856 

*  Refined  in  the  United  States  from  imported  Mexican  petroleum, 
f  There  are  discrepancies  in  the  figures  in  the  report. 

by  mineral  matter,  0.3  per  cent;  mineral  matter,  27.2  per  cent; 
water  of  hydration  in  clay  and  silicates,  4.3  per  cent. 

Trinidad  land  asphalt  reached  the  places  where  it  is  found 
either  by  overflowing  from  the  lake  or  by  intrusion  into  the  soil 
from  the  same  subterranean  source  that  supplies  the  lake  asphalt. 


120 


AMERICAN   HIGHWAY  ASSOCIATION 


Its  character  is  much  affected  by  the  effect  of  the  weathering  to 
which  it  has  been  subjected.  Clifford  Richardson  states  that 
refined  land  asphalt  of  good  quality  differs  from  the  lake  supply 
byits  higher  specific  gravity  due  to  the  larger  amount  of  mineral 
matter  it  contains,  by  a  higher  softening  or  melting  point,  and 
a  somewhat  lower  percentage  of  bitumen  and,  in  consequence  of 
these  facts,  a  much  greater  hardness  at  all  temperatures.  Land 
asphalt  requires  much  more  paraffin  flux  than  lake  asphalt,  and 
asphaltic  oil  fluxes  offer  certain  advantages  over  paraffin  fluxes 
for  use  with  land  asphalt. 

Composition  of  Refined  Trinidad  and  Bermudez  Asphalts 
(Clifford  Richardson) 


TRINIDAD 

BERMTTDEZ 

Specific  gravity  at  77°F.  (25°C.)          .    .  . 

1    40 

1  08 

Streak  

Blue  black 

Black 

Lustre  

Dull 

Bright 

Structure  

Homogeneous 

Uniform 

Fracture 

Semi-con- 

Semi-con- 

Hardness                                        

choidal 
2 

choidal 
Soft 

Melts  ..                                         

235°F.(113°C.) 

183°F.(84°C.) 

Penetration  at  77°F.  (25°C.)     

4 

20 

Loss  at  325°F.  (163°C.),  7  hours  

1.1% 

3% 

Character  of  residue  

Smooth 

Smooth 

Loss  at  400°F  (205°C  )  7  hours 

4  0% 

8  2% 

Character  of  residue 

Blistered 

Wrinkled 

Bitumen  soluble  in  CSg 

56  5% 

94.4% 

Bitumen  retained  by  mineral  matter 

0  3% 

Mineral  matter  

38.5% 

3.6% 

Water  of  hydration 

4  2% 

Vegetable  matter 

2  0% 

Bitumen  soluble  in  88°  naphtha 

35  6% 

62  2% 

Percentage  of  total  bitumen  which  above  is 
Soluble  bitumen  removed  by  HjSO^  

63.1% 
61.3% 

65.4% 
62.4% 

Saturated  hydrocarbons  in  total  bitumen.  . 
Pure  bitumen  soluble  in  C  Cl^ 

24.4% 
100  0% 

24.4% 
99  5% 

Fixed  carbon 

10  8% 

13.4% 

Bermudez  Asphalt. — Bermudez  asphalt  comes  from  a  pitch  lake 
in  Venezuela  about  30  miles  from  the  coast  in  an  air  line.  The 
lake  is  about  1J  miles  long,  1  mile  wide,  of  irregular  shape  and 
covers  about  900  acres.  It  is  covered  with  a  crust  from  a  few 
inches  to  2  feet  thick,  having  some  grass  and  shrubs,  with  a  few 
palms,  and  the  pitch  is  visible  on  the  surface  in  but  few  places. 
It  is  very  wet,  so  that  excavations  fill  with  water  and  it  is  diffi- 
cult to  excavate  the  pitch,  which  has  an  average  depth  of  4  feet. 
The  deposit  is  probably  formed  by  the  exudation  of  a  large  quan- 
tity of  soft  maltha.  The  asphalt  from  the  lake  varies  greatly  in 


ASPHALT  AND   NATIVE    SOLID   BITUMENS  121 

the  amount  of  water  it  contains,  which  fluctuates  between  11 
and  46  per  cent.  This  water  is  not  emulsified  with  the  bitumen 
but  is  adventitious  surface  water.  The  material  for  industrial 
use  is  selected,  and  when  refined  has  the  composition  given  in 
the  accompanying  table,  which  also  gives  the -composition  of  refined 
Trinidad  asphalt. 

Meaning  of  Analyses. — The  significance  of  most  of  the  terms 
used  in  this  table  are  explained  in  the  section  on  Petroleum.  The 
new  terms  are  the  following: 

Streak  is  the  color  of  a  rubbed  or  scratched  surface. 

Hardness  is  stated  in  terms  of  Mohr's  scale,  in  which  1  is  the 
hardness  of  talc,  2  that  of  rock  salt,  3  that  of  calcite,  4  that  of 
fluorite,  etc.  When  a  bitumen  is  softer  than  I  on  this  scale  its 
hardness  is  stated  by  its  behavior  in  a  penetration  test,  explained 
below. 

Melting  point  is  determined  by  an  arbitrary  test,  because 
bituminous  materials  are  made  up  of  a  mixture  of  hydrocarbons 
and  their  derivatives  and  can  not  have  a  true  melting  point,  such 
as  a  definite  compound  possesses. 

Penetration  is  determined  by  the  distance  that  a  needle  of 
specified  size  loaded  with  a  specified  weight  will  penetrate  into  a 
sample  of  the  material  in  a  specified  time.  Usually  a  No.  2 
needle  loaded  so  that  the  total  weight  is  100  grams  and  a  time 
period  of  5  seconds  is  employed,  but  a  50-gram  weight  and  a 
1-second  time  period  are  used  with  liquid  bitumens.  Prevost 
Hubbard  makes  the  following  statement  regarding  this  test: 

The  penetration  test  is  a  convenient  one  to  employ  for  identification 
and  control,  and  is  often  indicative  of  the  value  of  an  oil  or  asphalt  product 
for  construction  work.  While  the  test  for  bituminous  road  materials  is 
made  in  the  same  manner  as  in  asphalt  paving  work,  the  standards  for 
road  purposes  are  somewhat  different.  No  oil  product  should  be  employed 
in  macadam  construction  with  a  penetration  higher  than  25  mm.  when 
tested  at  25°C.  with  a  No.  2  needle  for  five  seconds  under  a  weight  of  100 
grams,  unless  it  possesses  the  property  of  hardening  considerably  when 
subjected  to  the  volatilization  test.  On  the  other  hand,  it  is  rarely  neces- 
sary to  require  a  penetration  as  high  as  that  for  asphaltic  cement  used  in 
the  topping  of  an  asphalt  pavement,  for  the  reason  that  the  upper  course 
of  a  macadam  road  has  much  greater  inherent  stability  than  the  sand 
course  of  the  asphalt  pavement.  A  penetration  of  from  10  to  15  mm.  is 
usually  considered  sufficient  for  road  work.  If  a  material  having  a  much 
lower  penetration  is  selected,  its  susceptibility  to  temperature  changes 
will  have  to  be  considered. 

Organic  matter  insoluble  is  a  term  of  uncertain  significance 
which  has  been  explained  by  Clifford  Richardson  as  follows : 

On  adding  together  the  percentages  of  bitumen  soluble  in  carbon  disul- 
phide  and  of  inorganic  matter  obtained  on  ignition,  the  sum  will  seldom 
amount  to  100.0.  The  difference  has  been  considered  for  many  years  as 


122  AMERICAN   HIGHWAY  ASSOCIATION 

organic  matter  not  bitumen  (insoluble).  This  maybe  true  in  exceptional 
cases,  but  recent  investigations  have  shown  that  it  is  not  at  all  so  in  many 
bitumens.  For  example,  in  Trinidad  asphalt  it  has  been  found  to  consist 
of  the  water  of  combination  of  the  clay  which  the  material  contains  and 
some  inorganic  salts  which  are  volatilized  on  ignition.  The  amount  of 
organic  matter  is  extremely  small.  In  other  cases,  it  may  consist  to  a 
considerable  extent  of  grass  and  twigs,  as  in  the  seepages  which  have  run 
out  over  sod.  On  the  whole,  therefore,  it  seems  desirable  not  to  describe 
it  by  any  definite  name,  but  merely  as  an  undetermined  difference. 

Pure  bitumen  soluble  in  CCU  (carbon  tetrachloride)  is  not 
usually  determined  unless  a  road  oil  has  been  badly  cracked  or  a 
solid  bitumen  like  grahamite  has  been  added,  so  that  the  per- 
centage of  hydrocarbons  insoluble  in  88°  naphtha  is  high.  The 
bitumens  insoluble  in  carbon  tetrachloride  but  soluble  in  carbon 
bisulphide  are  called  "carbenes." 

Other  Asphalts. — Maracaibo  asphalt  is  found  on  the  Limon 
River  about  50  miles  west  of  Maracaibo,  Venezuela.  According 
to  Clifford  Richardson  it  is  an  exudation  from  maltha  springs. 
When  carefully  refined  it  contains  from  92  to  97  per  cent  of 
bitumen  soft  enough  to  be  indented  by  the  finger  nail.  It  con- 
tains a  very  small  percentage  of  malthenes  and  has  a  higher  soften- 
ing point  than  either  Trinidad  or  Bermudez  asphalt. 

Cuban  asphalts  are  found  in  small  quantities  in  many  places 
on  the  island  and  what  little  use  of  them  is  made  in  the  United 
States  is  mainly  for  varnishes.  A  deposit  18  miles  from  Havana 
has  furnished  material  used  in  street  pavements. 

Asphaltic  materials  are  found  in  many  places  in  Mexico,  and 
some  of  them  have  been  developed  more  or  less.  What  is  usually 
known  among  roadbuilders  as  Mexican  asphalt  is  prepared  from 
the  malthas  and  petroleums  obtained  mainly  from  the  Tampico 
and  Tuxpan  district. 

Natural  asphalt  has  been  obtained  in  California  at  several 
places,  but  the  most  noted  deposits  are  no  longer  worked. 

Refining  natural  asphalt  consists  merely  in  driving  off  the 
water  it  contains  by  heating  the  material  to  about  325°F.  in 
large  tanks  containing  coils  of  pipes  through  which  steam  is 
passed.  In  the  bottom  of  the  tanks  are  steam  jets  which  agitate 
the  asphalt.  The  vegetable  impurities,  if  any,  are  skimmed  from 
the  top.  The  refined  asphalt  is  drawn  off  while  it  is  liquid  into 
barrels  for  shipment.  When  it  is  to  be  used,  it  is  melted  with  a 
residuum  flux. 

Solid  Bitumens  not  Asphalts. — Gilsonite  is  a  hard,  brittle  bitu- 
men with  a  reddish  brown  streak  and  a  conchoidal  fracture, 
obtained  mainly  from  Utah  and  Colorado.  It  is  sold  in  two 
grades,  gilsonite  selects  and  gilsonite  seconds,  the  former  being 
the  more  pure.  Gilsonite  from  different  mines  varies  consider- 
ably, and  some  of  it  is  of  little  value  for  use  in  paving  mixtures. 


ASPHALT  AND   NATIVE   SOLID   BITUMENS 


123 


Grahamite  is  a  hard,  brittle  bitumen  with  a  black  streak, 
otherwise  resembling  gilsonite  in  appearance.  Its  softening 
point  is  very  high  and  not  yet  definitely  determined.  It  is 
obtained  mainly  from  Oklahoma. 

Properties  of  Gilsonite  and  Grahamite 
(Clifford  Richardson,  The  Modern  Asphalt  Pavement} 


GILSC 

JUTE 

GRAHAMITE 

Specific  gravity,  78°/78°F.  .  .  . 
Streak  

1.044 
Brown 

1.049 
Brown 

1.171 
Black 

Lustre  

Lustrous 

Lustrous 

Dull 

Fracture 

Sub-con- 

Sub-con- 

Hackly 

Hardness  

choidal 

2 

choidal 
2 

Brittle 

Softens    

260°F. 

300°F. 

Intumesces 

Flows     

275°F. 

325°F. 

Intumesces 

Loss,  325°F.,  7  hours  

0.9% 

2.3% 

0.1% 

Loss,  400°F.,  7  hours  

1.2% 

4.0% 

0.5% 

Bitumen  soluble  in  CSz  

99.0% 

99.9% 

94.1% 

Insoluble  organic  matter  .... 
Mineral  matter  

0.0% 
0.0% 

0.0% 

0.1% 

0.2% 

5.7% 

Bitumen  soluble  88°  naphtha 
Soluble  bitumen  removed  by 
H2SO4  

47.2% 
87.7% 

15.9% 
71.8% 

0.4% 
25.0% 

Total  bitumen  as  saturated 
hydrocarbons 

5  9% 

4.5% 

0.32% 

Bitumen  soluble  in  62°  naph- 
tha 

67  4% 

30  3% 

0.7% 

Bitumen  insoluble  in  CCU  .  . 
Fixed  carbon 

0.0% 
13  0% 

0.4% 
13.4% 

68.7% 
53.3% 

Manjak  resembles  grahamite  and  is  obtained  from  Barbadoes 
and  South  America.  Its  lack  of  uniformity  and  its  high  price  have 
prevented  any  large  use  of  it  for  American  pavements,  although 
it  is  used  successfully  in  preparing  other  materials. 

Fluxing  Solid  Bitumens. — Paving  materials  are  made  from  solid 
bitumens  by  fluxing  them  with  petroleum  residuums  by  two 
methods.  In  the  first  method  the  residuum  is  heated  to  above 
the  temperature  at  which  the  solid  bitumen  melts  and  the  latter 
is  then  added.  Grahamite  does  not  melt  but  intumesces  and  the 
residuum  to  flux  it  must  be  raised  to  an  exceptionally  high  tem- 
perature. The  mixture  is  agitated  until  the  bitumen  is  all 
melted  and  the  combined  material  is  of  uniform  quality. 

In  the  second  method,  the  residuum  is  heated  to  about  350°F. 
and  air  is  then  blown  through  it  for  six  to  forty  hours,  depending 
upon  the  quality  of  the  old  and  the  properties  desired  in  the  fin- 
ished product.  As  soon  as  it  reaches  the  proper  consistency  the 
blowing  is  stopped  and  enough  solid  bitumen  mixed  with  it  to 
give  a  paving  material  having  the  required  properties. 


ASPHALTIG  MATERIALS  FOR  ROADS' 

The  selection  of  bituminous  materials  for  road  purposes  should 
be  based  upon  the  local  climatic  conditions,  the  volume  and 
character  of  the  traffic,  the  character  of  the  stone  to  be  used, 
and  the  type  of  road  to  be  constructed  or  maintained.  Such 
conditions  manifestly  call  for  expert  advice.  The  requirements 
of  several  state  highway  departments  are  given  here  merely  as 
indicating  the  way  in  which  specialists  have  met  the  needs  of 
their  respective  localities.2 

Some  of  the  requirements  for  road  oils  can  be  met  by  a  few 
crude  asphaltic  petroleums.  Pre*yost  Hubbard  gives  the  accom- 
panying analysis  of  a  crude  California  petroleum  of  this  char- 
acter. This  oil  contained  a  small  amount  of  water,  and  care  in 
heating  it  would  be  necessary  to  prevent  foaming.  Hubbard 
says  that  "this  oil  is  capable  of  increasing  greatly  in  consistency 
after  application  and  would  serve  as  an  excellent  binding  medium." 

1  Revised  by  Pr6vost  Hubbard,  chief  of  road  materials  tests  and  re- 
search, United  States  Office  of  Public  Roads. 

2  Among  the  engineers  to  whom  this  chapter  was  submitted  was  F.  H. 
Joyner,  Road  Commissioner  of  Los  Angeles  County,  California,  who  pre- 
pared the  following  comment,  which  illustrates  forcibly  the  necessity  of 
the  services  of  a  specialist  in  extensive  road  improvements: 

"From  a  study  of  the  notes  you  submitted  made  by  my  assistants  and 
myself,  and  from  reports  of  the  chemist  and  chief  road  oiler,  we  reached 
the  decision  that  our  study  and  conclusions  on  what  we  call  road  oils  are 
of  value  only  here  in  California,  where  we  use  only  the  native  oils.  While 
there  is  much  in  the  notes  that  would  not  be  applicable  to  our  California 
oils  or  asphalts,  I  do  not  believe  it  would  be  necessary  or  proper  to  propose 
any  changes  in  the  notes." 

The  following  statement  by  W.  Arthur  Brown,  chemist  of  the  Los 
Angeles  county  road  department,  explains  the  views  mentioned  by  Mr. 
Joyner : 

"The  desirable  constituent  of  a  first-class  road  is  asphalt.  The  asphalt 
carpet  coat  demands  an  oil  that  contains  the  highest  grade  of  asphalt.  It 
also  demands  that  this  asphalt  be  thin  enough  to  spread  well.  It  should 
enter  all  the  interstices  of  the  road  surface.  When  the  lighter  constituents 
of  the  oil  have  served  their  purpose,  namely,  that  of  carrier  and  distribu- 
tor, they  are  no  longer  needed,  in  fact,  they  are  not  needed  except,  possi- 
bly, in  very  small  amount.  They  should  then  be  of  such  a  nature  that  they 
will  volatilize  readily.  We  do  not  wish  a  possible  volatile  constituent  that 
is  solid  or  nearly  so  in  cold  weather  but  thin  and  acting  as  a  fluxing  agent 
in  hot  weather. 

The  specification  of  the  Los  Angeles  county  highway  department  is  a 
departure  from,  and  simpler  than,  the  older  ones  requiring  fixed  carbon, 
asphaltene,  viscosity,  float  test,  loss  on  heating  during  a  certain  number 
of  hours  at  a  specified  temperature,  ductility  test,  etc.  This  specification 
requires  that  the  oil  be  reduced  on  the  Brown  evaporator  in  a  specified 
time.  This  test  determines  the  percentage  of  asphalt  and  insures  the 

124 


ASPHALTIC   MATERIALS   FOB  ROADS  125 

Crude  California  Petroleum  Adapted  for  Road  Work 
(From  Provost  Hubbard's  Dust  Preventives  and  Road  Binders) 

Character Black,  viscous,  sticky. 

Specific  gravity  25°/25°C 0.984 

Flash  point,  degrees  C 160.0 

Loss  at  100°C.,  7  hours,  per  cent 5.25 

Character  of  residue More  viscous  than  crude 

Loss  at  163°C.,  7  hours,  per  cent 16.4 

Character  of  residue Sticky,  very  viscous 

Loss  at  205°C.,  7  hours,  per  cent 30.0 

Character  of  residue Solid,  not  brittle 

Soluble  in  CS2,  per  cent 99.77 

Organic  matter  insoluble,  per  cent 0.12 

Inorganic  matter,  per  cent 0.11 

Bitumen  insoluble  in  86°  naphtha,  per  cent 9.8 

Fixed  carbon,  per  cent 2.05 

Viscosity,  mentioned  in  this  table,  is  explained  by  PreVost 
Hubbard  as  follows: 

If  it  is  desired  to  apply  a  rpad  binder  at  a  given  temperature,  as  for 
instance  when  it  is  to  be  heated  by  means  of  steam,  a  determination  of  its 
viscosity  at  that  temperature  is  often  of  value.  The  test  also  serves  as 
a  means  of  identification.  When  a  viscous  material  is  to  be  cut  with  one 
of  lower  viscosity  in  order  to  bring  it  to  a  proper  consistency  for  applica- 
tion, the  actual  viscosity  of  the  mixture  should  be  ascertained  and  not 
calculated  from  that  of  the  two  constituents  for  the  reason  that  this  prop- 
erty is  not  additive. 

In  reporting  the  results  of  the  test,  the  temperature  of  the 
material,  the  quantity  used  in  testing,  and  the  time  in  seconds 
taken  by  the  material  in  flowing  through  a  short  tube  of  standard 
dimensions  in  what  is  called  an  Engler  viscosimeter,  are  recorded. 
The  longer  the  period  of  time  taken  by  the  material  in  flowing 
through  the  tube,  the  greater  its  viscosity. 

The  float  test  is  employed  in  determining  the  relative  con- 
sistency of  very  viscous  materials.  The  results  are  reported  in 
seconds  of  time  that  a  float  containing  the  material  under  test 
will  remain  floating  in  water  at  a  stated  temperature.  It  is  con- 
sidered a  very  useful  test  in  controlling  the  preparation  of  road 

volatile  oil  being  01  such  a  nature  that  it  will  leave  the  oil  when  once  it  is 
applied  on  the  road.  The  percentage  of  asphalt  is  also  much  nearer  the 
actual  in  the  oil  than  by  the  methods  of  heating  in  an  oven  at  a  lower 
temperature.  These  specifications  also  require  a  stickiness  test.  This 
stickiness  test,  made  on  the  Brown  adhesivemeter,  when  interpreted  in 
accordance  with  the  entire  specifications,  especially  with  the  time  to  reduce 
to  asphalt,  determine  whether  the  oil  has  sufficient  binding  properties  to 
hold  the  particles  from  displacement  from  each  other  and  from  the  base. 
The  stickiness  and  loss  are  standardized  against  road  oils  found  on  the 
market  throughout  California.  The  results  of  the  tests  have  been  carefully 
compared  with  actual  service  results,  which  are  in  accord  with  laboratory 
results  in  every  case  so  far  known." 


126 


AMERICAN  HIGHWAY  ASSOCIATION 


oils  from  given  materials,  for  by  continuing  the  heating  until 
the  residue  gives  a  predetermined  result  in  the  float  test,  a  uni- 
form product  will  be  obtained. 

The  ductility  test  shows  the  distance  in  centimeters  that  a 
briquette  of  the  material  will  stretch  before  breaking,  when 
pulled  at  the  rate  of  5  centimeters  per  minute.  The  briquette 
is  1  cm.  square  at  the  smallest  section  and  has  a  cross-section 
of  2  square  cm.  at  the  clips,  which  are  3  cm.  apart. 

State  Requirements  for  Asphaltic  Materials  for  Penetration  Roads 


ILLINOIS 

OHIO 

NEW 
YORK 

PENNSYL- 
VANIA 

Grade  A 

Grade  B 

Grade 
A-l 

Grade 
A 

Specific  gravity,  25°/25°C  

1.000+ 
163 

50 
5-12* 

6 
Smooth 

0.97-1.00 
200 

15 

5-8 

2 

Smoothf 

99.5 

0.97+ 
180 

30 
9-16} 

5 
§ 

0.97+ 
190 

40 
14-19 

5 

§ 

Flash  point,  degrees  C.,  min  
Ductility  at  25°C.,  centimeters, 
min        ...                       

45 
9-15 
5 

Penetration,    100    gr.,    5    sec., 
25°C.,  mm.,  min  
Loss  at  163°C.,  5  hrs.,  per  cent, 
max 

Character  of  residue 

Bitumen   soluble   in   €82,    per 
cent,  min       .              ... 

99.0 

Pure  bitumen  products  

99.5 
95.0 
80.0 
65.0 

72-85 

99.5 
95.0 
81.0 
66.0 

72-85 
98.9+ 
8-16 

99.5 
96.0 
81.0 
66.0 

70-88A 

Bermudez  products  

Cuban  products  

Trinidad  products  

98.5 

Solubility  in  86°  naphtha,  per 
cent 

72-80 
99.4+ 
7-14 

Solubility  in  CCU,  per  cent.. 

Fixed  carbon,  per  cent.  .  . 

8-16 

*  8-12  for  material  with  90  per  cent  total  bitumen,  7-10  for  material 
with  80  per  cent  to  90  per  cent  bitumen  and  5-8  for  Trinidad  material 
having  less  than  80  per  cent  bitumen. 

t  Penetration  of  residue  at  least  60  per  cent  of  that  of  the  original 
material. 

}  9-12  for  pure  bitumen  products,  12-16  for  fluxed  native  asphalts. 

§  Penetration  of  residue  at  least  half  that  of  original  material. 

A  In  76°  naphtha. 

NOTE — Illinois  specifies  a  brittleness  test  as  follows:  "A  cylindrical 
prism  of  the  bituminous  binder  1  cm.  in  diameter,  after  being  maintained 
at  a  temperature  of  5°C.  (41  °F.)  for  20  minutes,  shall  bend  180  degrees 
at  any  point  without  checking  or  breaking."  New  York  specifies  a  tough- 
ness test  as  follows:  "It  (the  bituminous  material)  shall  show  a  toughness 
at  32°F.  not  less  than  15  cm.  Toughness  is  determined  by  breaking  a 
cylinder  of  the  material  If  inches  in  diameter  by  If  inches  in  height  in  a 
Page  impact  machine.  The  first  drop  of  the  hammer  is  from  a  height  of 
5  cm.  and  each  succeeding  blow  is  increased  by  5  cm."  New  York  also 
specifies  a  maximum  of  4.7  per  cent  of  paraffin. 


ASPHALTIC  MATERIALS   FOR  ROADS 


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128 


AMERICAN   HIGHWAY   ASSOCIATION 


State  Requirements  for  Asphaltic  Materials  for  Surfacing 


NEW  YORK 

OHIO 

Grade 
H.  O. 

Grade 
C.  O. 

Grade 
H.  O. 

Grade 
M.  O. 

Grade  C.  O 

Specific  gravity  25°/25°C 

0.96 

163 

* 

10 

0.93 

52 
30 

0.96 

0.93 

0.91 

Flash  Point  degrees  C 

Ductility  at  20°C    cm             ... 

'  '  30  '  ' 

Sticky 
99.5 

90-98 
3 

Loss  at  163°C.,  5  hours,  per  cent  . 
Character  of  residue  

5 

25 

Bitumen  soluble  in  CS2,  per  cent. 
Solubility  in  86°  naphtha,   per 
cent 

99.5 

75.90f 
6^14 

4.7 

99.5 

80-95  f 
10 
4.0 

99.5 

80-94 
6 

99.5 

85-97 
3.5 

Fixed  carbon,  per  cent 

Paraffin  scale  per  cent 

*  The  residue  after  evaporation  to  10  mm.  penetration  at  a  tempera- 
ture not  exceeding  500°F.,  must  amount  to  85  to  95  per  cent  of  the  original 
volume  and  have  a  ductility  of  at  least  25  cm. 

t  In  76°  naphtha. 

j  The  residue  after  evaporation  to  10  mm.  penetration  at  a  temperature 
not  exceeding  500°F.  must  amount  to  50  to  65  per  cent  of  the  original 
volume  and  have  a  ductility  of  at  least  25  cm. 

NOTE — New  York  specifies  the  following  toughness  test:  Grade  H.  O. 
shall  show  a  toughness  at  32°F.  not  less  than  20  cm.  determined  by  the 
Page  impact  test.  Ohio  requires  a  viscosity  of  10  to  60  at  100°C.  for  50  cc. 
for  Grade  H.  O.,  40  to  80  at  50°C.  for  50  cc.  for  Grade  M.  O.,  and  5  to  12 
at  50°C.  for  50  cc.  for  Grade  C.  O. 

Shipping  Road  Oil. — Small  quantities  of  road  oil  are  shipped  in 
tight  wooden  50-gallon  barrels,  such  as  are  used  for  shipping 
molasses,  or  in  steel  barrels.  These  barrels  make  the  oil  cost  2 
to  3  cents  a  gallon  more  than  the  price  for  the  oil  itself.  Unin- 
jured empty  barrels  can  generally  be  resold  to  the  shipper. 
Heavy  oil  is  troublesome  to  remove  from  barrels,  and  they  are 
usually  dumped  into  the  open  heating  kettles  and  broken  up. 
When  the  oil  is  warm  the  broken  pieces  of  wood  are  raked  out 
and  used  for  fuel.  If  there  is  no  heating  kettle  on  the  job,  the 
barrels  of  heavy  oil  must  be  kept  close  to  a  fire  or  in  a  very  warm 
room  before  the  oil  can  be  poured  from  them  into  the  distributor. 

Larger  quantities  of  oil  are  shipped  in  tank  cars,  holding  8000 
or  12,000  gallons.  Where  a  large  amount  of  oil  is  to  be  used 
annually  near  any  railway,  it  will  be  desirable  for  the  officials  to 
supply  a  tank  into  which  the  oil  can  be  run  as  soon  as  the  car 
arrives.  The  season  for  roadwork  is  limited  and  during  it  there 
is  a  brisk  demand  for  tank  cars.  The  oil  company  which  loses 
the  service  of  a  car  for  a  week  or  ten  days,  while  it  stands  on  a 
siding  waiting  to  be  emptied,  is  obliged  to  add  an  equivalent 
item  to  its  overhead  expense,  and  the  road  district  which  provides 
for  prompt  discharge  of  tank  cars  is  in  a  position  to  demand, 


ASPHALTIC   MATERIALS   FOR  ROADS 


129 


and  will  probably  get,  quotations  shaded  somewhat  to  recognize 
its  sense  of  business  fairness. 

If  oil  must  be  used  hot,  a  f  or  1-inch  steam  connection  must 
be  made  with  the  heating  coils  of  the  tank  car.  For  this  reason, 
the  car  is  often  spotted  on  a  siding  near  an  electric  station  or 
mill,  but  the  steam  can  also  be  furnished  by  a  road  roller,  trac- 
tion engine  or  other  convenient  source.  It  will  take  from  twelve 
to  twenty-four  hours  to  heat  a  tankful  of  heavy  oil  to  150°  to 
170°F.,  which  is  high  enough  to  allow  it  to  be  pumped.  The 
temperature  can  be  increased  after  that  in  the  distributor.  The 
amount  of  steam  supplied  to  the  heating  coils  of  the  car  is  regu- 
lated by  a  valve  on  the  exhaust  pipe  of  the  coil,  which  is  adjusted 
to  prevent  a  waste  of  steam.  As  some  road'  oils  have  a  low  flash 
point,  great  care  must  be  taken  to  prevent  any  oil  coming  in  con- 
tact with  a  flame.  The  temperature  of  the  oil  should  be  tested 
from  time  to  time  with  a  thermometer,  to  see  that  it  is  not  over- 
heated. If  there  is  any  water  in  the  oil  it  will  give  a  great  deal 
of  trouble  if  heated  quickly,  and  if  foaming  is  detected  the  rate 
of  heating  should  be  checked  at  once. 

Specific  Gravities,  Degrees  Baume,  Weights  in  Pounds  per  Gallon  and  Volume 

in  Gallons  per  Pound  of  Oils  at  60°F.  Having  Specific 

Gravities  Exceeding  LOO 


SPECIFIC 
GRAVITY 

DEGREES 
BAUME 

POUNDS 
PER  GALLON 

GALLONS 
PER  POUND 

SPECIFIC 
GRAVITY 

DEGREES 
BAUME 

POUNDS 
PER  GALLON 

GALLONS 
PER  POUND 

1.00 

0.00 

8.328 

0.1201 

1.15 

18.91 

9.577 

0.1021 

1.01 

1.44 

8.411 

0.1189 

1.16 

20.00 

9.660 

0.1009 

1.02 

2.84 

8.495 

0.1177 

1.17 

21.07 

9.744 

0.0997 

1.03 

4.22 

8.578 

0.1165 

1.18 

22.12 

9.827 

0.0985 

1.04 

5.58 

8.661 

0.1153 

1.19 

23.15 

9.910 

0.0973 

1.05 

6.91 

8.744 

0.1141 

1.20 

24.17 

9.994 

0.0961 

1.06 

8.21 

8.828 

0.1129 

1.21 

25.16 

10.077 

0.0949 

1.07 

9.49 

8.911 

0.1117 

1.22 

26.15 

10.160 

0.0937 

1.08 

10.74 

8.994 

0.1105 

1.23 

27.11 

10.243 

0.0925 

1.09 

11.97 

9.078 

0.1093 

1.24 

28.06 

10.327 

0.0913 

1.10 

13.18 

9.161 

0.1081 

1.25 

29.00 

10.410 

0.0908 

1.11 

14.37 

9.244 

0.1069 

1.26 

29.92 

10.494 

0.0889 

1.12 

15.54 

9.327 

0.1057 

1.27 

30.83 

10.577 

0.0877 

1.13 

16.68 

9.411 

0.1045 

1.28 

31.72 

10.660 

0.0865 

1.14 

17.81 

9.494 

0.1033 

1.29 

32.60 

10.743 

0.0853 

NOTE:  For  a  similar  table  of  oils  of  specific  gravities  less  than  1.00 
see  page  112. 

Pumping  Road  Oil. — In  order  to  remove  the  oil  from  the  tank 
car  to  the  distributors,  some  form  of  pump  is  generally  necessary, 
for  it  is  not  often  that  the  car  can  be  placed  on  a  siding  or  trestle 
high  enough  to  allow  it  to  be  emptied  by  gravity. 


130  AMERICAN   HIGHWAY  ASSOCIATION 

If  a  lift  pump  set  in  the  top  of  the  car  is  used,  it  should  be  a 
3  or  4-inch  size.  With  it  one  man  can  fill  a  600-gallon  dis- 
tributor in  twenty  minutes. 

In  many  cases  a  hose  or  pipe  is  connected  to  the  bottom  of 
the  car  and  run  to  an  oil  pump,  operated  by  a  steam  or  gasoline 
engine,  which  forces  the  oil  into  the  distributor.  A  1J  or  2-inch 
power-driven  rotary  pump  will  deliver  600  gallons  in  ten  to  fif- 
teen minutes.  These  pumps  work  with  either  hot  or  cold  oil. 
A  water  tank  pump  can  be  used  with  cold  oil  but  hot  oil  will  ruin 
the  valves  speedily.  A  2-inch  suction  tank  pump  will  fill  a  600- 
gallon  tank  in  thirty  to  forty  minutes. 

The  hose  used  in  the  connections  between  the  pump  and  the 
bottom  of  the  tank  car  should  be  as  short  as  possible  because  the 
oil  often  destroys  it  rapidly.  It  is  desirable  to  have  a  cut-off 
valve  in  the  connection  pipe.  When  everything  is  coupled  ready 
for  use,  the  discharge  valve  in  the  bottom  of  the  car  is  raised  by 
means  of  a  vertical  stem  running  up  to  the  dome  of  the  car,  and 
the  flow  of  oil  is  controlled  by  the  cut-off  valve,  for  the  manipu- 
lation of  the  tank  valve  is  quite  troublesome. 

Heating  Road  Oil. — As  the  fixed  and  operating  charges  at  an 
oil  storage  plant  are  about  the  same  irrespective  of  the  amount 
of  oil  delivered  into  distributors,  it  is  desirable  to  load  as  many 
carts  daily  as  practicable,  in  order  to  reduce  the  unit  cost  of  such 
work.  In  California,  where  large  amounts  of  oil  are  used  in  sur- 
facing concrete  roads,  oil  stations  have  been  designed  with  par- 
ticular attention  to  effecting  such  economics.  It  is  considered 
desirable  to  have  the  oil  at  a  temperature  of  300°  F.  when  it  is 
applied,  so  it  is  heated  to  325°  for  delivery  within  10  miles  and 
350°  for  longer  deliveries. 

The  oil  is  discharged  from  the  cars  into  storage  tanks  or  pits 
holding  10,000  to  25,000  gallons.  These  contain  steam  coils  to 
warm  the  oil  sufficiently  to  enable  it  to  be  pumped  into  a  circu- 
lating tank  holding  2000  to  3000  gallons,  where  it  is  heated 
further  by  steam  coils.  The  oil  is  then  pumped  through  a  heater 
and  back  into  the  circulating  tank  until  its  temperature  is  about 
200°,  after  which  the  temperature  of  the  heater  is  raised  and  the 
oil  pumped  through  it  into  the  distributor.  The  whole  operation 
takes  one  and  one-half  hours. 

The  heater  resembles  a  return  tubular  boiler.  The  furnace 
has  a  fire  brick  arch  and  walls  and  is  heated  by  oil  burners.  The 
heated  gases  pass  over  the  furnace  arch  in  a  chamber  formed  of 
ordinary  brick  masonry,  and  finally  escape  through  a  steel  stack. 
The  oil  is  pumped  through  a  multiple  grid  of  3-inch  pipes.  The 
design  is  made  on  the  assumption  that  with  furnace  temperatures 
of  1800°  to  2000°,  1  square  foot  of  heating  surface  will  transmit 
3  British  thermal  units  per  hour  per  degree  of  change  in  temperature. 


ASPHALTIC   MATERIALS  FOR    ROADS 


13J 


Volume  of  Oil  at  60°F.  Equivalent  to  Unit  Volume  at  Stated  Temperatures  in 
Fahrenheit  Degrees 


0°F 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

1.000 

0.996 

0.992 

0.988 

100 
200 
300 
400 

0.984 
0.947 
0.912 
0.881 

0.980 
0.943 
0.909 
0.877 

0.977 
0.940 
0.906 
0.875 

0.973 
0.936 
0.903 
0.871 

0.969 
0.933 
0.899 
0.868 

0.965 
0.929 
0.896 
0.865 

0.962 
0.926 
0.893 
0.862 

0.958 
0.922 
0.890 
0.859 

0.954 
0.919 
0.886 
0.856 

0.951 
0.916 
0.883 
0.853 

NOTE  :  This  table  is  based  on  the  assumption  that  the  volume  of  oil 
increases  0.4  per  cent  for  every  increase  of  10°F.  above  60°.  This  rule 
is  exactly  applicable  only  to  some  oils.  In  Los  Angeles  County,  Cal.,  the 
rate  of  increase  in  volume  is  taken  at  0.3  per  cent  in  the  specifications  of 
the  county  road  department. 

Purchasing  Oil. — Oil  increases  in  volume  from  0.3  to  0.4  per 
cent  for  each  10°F.  rise  in  its  temperature.  The  oil  is  bought 
on  the  basis  of  its  volume  at  60°F.  and  if  measured  at  any  other 
temperature  its  volume  must  be  computed,  or,  in  the  case  of  an 
oil  having  an  increase  in  volume  of  0.4  per  cent  per  10°F.,  the 
accompanying  table  will  give  the  volume  at  60°  with  a  minimum 
amount  of  figuring.  To  use  it,  multiply  the  tabular  number 
for  the  temperature  at  which  the  measurement  was  made  by 
the  measured  quantity  of  oil.  For  example  1,100  gallons  of  oil 
at  375°F.  multiplied  by  0.888  gives  978  gallons  as  the  volume 
at  60°F.  If  the  rate  of  increase  per  10°F.  was  0.3  per  cent,  the 
volume  at  60°F.  would  be  995  gallons. 


TAR  AND  TAR  PRODUCTS1 

The  tar  used  in  roadbuilding  is  obtained  by  refining  the  crude 
tar  produced  in  the  destructive  distillation  of  coal,  in  making  en- 
riched water  gas  and  in  certain  classes  of  coke  ovens.  It  is  a  com- 
plex mixture  of  many  hydrocarbons  and  is  not  a  simple  chem- 
ical substance. 

In  a  city  gashouse,  gas  is  produced  by  heating  coal  in  retorts 
usually  about  8  feet  long,  15  inches  high  and  18  inches  wide. 
The  tar  is  driven  off  with  the  gas  and  is  collected  for  the  most 
part  in  "hydraulic  mains"  which  act  as  water  seals  for  the  gas. 
The  gas  is  further  cooled  in  a  condenser,  where  more  tar  is  de- 
posited, and  the  remaining  tar  is  removed  in  a  tar  extractor 
and  scrubbers.  The  tar  obtained  at  each  stage  in  the  process 
is  different  from  that  obtained  at  the  other  stages,  but  all  of  it 
is  usually  run  into  large  wells,  where  the  accompanying  ammo- 
niacal  water  rises  and  is  drawn  off.  The  character  of  the  tar 
varies  greatly.  It  is  much  affected  by  the  temperature  at  which 
the  coking  is  conducted,  as  well  as  by  the  character  of  the  coal 
used.  High  temperatures  result  in  an  increase  in  the  amount  of 
free  carbon  in  the  tar,  and  this  increase  in  free  carbon  is  accom- 
panied by  an  increase  in  specific  gravity.  The  presence  of  ammo- 
niacal  water  with  oils  distilling  below  110°C.  is  stated  by  Pre- 
vost  Hubbard  to  be  the  distinguishing  features  of  all  crude  coal 
tars. 

Another  class  of  tar  is  obtained  from  by-product  coke  ovens. 
The  retorts  in  this  case  are  much  larger  but  are  operated  in  much 
the  same  way  as  the  retorts  of  illuminating  gas  plants,  except 
that  the  main  endeavor  is  to  produce  the  maximum  amount  of 
coke  instead  of  gas.  For  this  reason  the  temperatures  are  lower 
than  those  usually  employed  in  coal-gas  works  and  the  tar  is 
likely  to  have  a  comparatively  low  amount  of  free  carbon  and  a 
comparatively  high  amount  of  oils.  There  are  several  types  of 
by-product  coke  ovens,  and  some  produce  tars  better  suited  for 
road  work  than  other  types. 

Water  gas  is  made  by  passing  steam  over  hot  coal,  in  which 
process  no  tar  is  produced.  This  gas  is  a  mixture  of  hydrogen 
and  carbon  monoxide,  and  burns  with  a  flame  of  no  value  for 

1  Revised  by  Prevost  Hubbard,  chief  of  road  materials  tests  and  research, 
U.  S.  Office  of  Public  Roads. 

132 


TAR  AND   TAR   PRODUCTS  133 

illumination.  It  must  therefore  be  mixed  with  hydrocarbons, 
which  are  usually  obtained  by  cracking  a  grade  of  petroleum  dis- 
tillate called  gas  oil.  In  the  purification  of  this  enriched  or  "car- 
buretted"  gas,  tar  is  obtained  which  is  called  water-gas  tar. 
It  is  lighter  than  coal  tar  and  the  water  it  contains  is  practically 
free  from  ammonia,  which  is  an  identifying  characteristic  of  this 
material.  It  has  a  comparatively  high  amount  of  heavy  oil  and 
a  low  amount  of  pitch. 

In  some  gas  works  both  coal  gas  and  water  gas  are  made  and  the 
tar  from  both  processes  are  collected  together,  resulting  in  mixtures 
which  may  vary  greatly  in  composition. 

The  crude  tar  is  stored  in  tanks  at  the  refineries,  each  class 
by  itself.  As  much  water  is  removed  by  settling  as  is  possible, 
since  this  is  the  cheapest  method  of  getting  rid  of  it.  After  set- 
tling, the  tar  is  pumped  into  a  still.  Sometimes  the  tars  from  sev- 
eral sources  are  mixed  so  that  a  product  with  certain  character- 
istics can  be  obtained  which  are  unattainable  by  refining  tar  from 
one  source.  The  stills  are  set  in  brick  like  horizontal  boiler  shells 
and  are  heated  very  carefully  at  first  to  prevent  the  water  in  the  tar 
from  causing  foaming.  The  vapors  from  the  still  are  liquified  in 
condensers.  Water  and  light  oils  are  first  driven  off,  then  inter- 
mediate oils  and  finally  heavy  oils.  The  road  materials  are  ob- 
tained from  the  residuum.  The  distillation  must  be  stopped 
early  if  a  light  road  tar  is  desired,  while  the  process  is  carried 
much  further  if  a  binder  is  desired.  In  the  final  stages,  the  con- 
tents of  the  still  are  agitated  by  jets  of  air  to  prevent  coking. 

The  composition  of  several  crude  tars  and  of  the  heavy  pitches 
made  by  refining  them  is  given  in  the  accompanying  table.  The 
figures  must  not  be  considered  more  than  representative  of  gen- 
eral characteristics,  for  individual  tars  in  the  same  class  vary 
greatly. 

Tar  products  for  road  purposes  are  called  "straight-run"  when 
they  are  the  residuums  left  after  refining  crude  tars  to  the  degree 
which  will  furnish  a  material  of  suitable  composition,  and  "cut- 
back" when  they  are  made  by  fluxing  a  hard  pitch  with  a  lighter 
distillate. 

The  effect  of  free  carbon  in  tar  upon  its  utility  for  road  purposes 
has  been  a  subject  of  protracted  controversy.  Philip  P.  Sharpies 
makes  this  comment: 

Experience  has  seemed  to  settle  that  a  moderate  amount  of  free  carbon 
is  beneficial  in  a  road  tar,  thus  bearing  out  the  practical  experience  gained 
in  the  use  of  coal  tar  materials  in  other  directions.  At  the  same  time,  an 
excess  of  free  carbon  is  not  desirable,  since  it  tends  to  make  the  material 
difficult  to  work  and  also  reduces  to  a  considerable  degree  the  amount  of 
true  bitumen  available.  On  the  other  hand,  a  certain  percentage  of  free 
carbon  seems  to  enhance  the  binding  power  of  the  refined  tar.  The  upper 


134 


AMERICAN   HIGHWAY   ASSOCIATION 


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TAR  AND   TAR   PRODUCTS  135 

limit  may  perhaps  be  set  at  25  per  cent  for  a  binder  and  perhaps  22  per  cent 
for  a  tar  used  for  hot  surface  application.  The  lower  limits  on  these  classes 
of  materials  should  certainly  not  be  less  than  12  per  cent  for  binder  mate- 
rials and  10  per  cent  for  hot  surfacing  materials.  With  cold  surfacing 
materials  the  free  carbon  is  necessarily  much  lower,  as  its  presence  in  large 
quantities  reduces  the  penetration.  With  cold  surfacing  materials  4  per 
cent  may  be  placed  as  a  desirable  minimum. 

Prevost  Hubbard  makes  the  following  comments  on  free  car- 
bon in  his  Dust  Preventives  and  Road  Binders: 

In  tars  of  the  same  consistency,  those  of  low  carbon  contents  have  a 
greater  inherent  binding  strength  than  those  of  high-carbon  contents. 
In  tars  whose  bitumen  contents  are  of  the  same  consistency  those  of  high 
carbon  contents  have  a  greater  inherent  binding  strength  than  those  of  low 
carbon  contents,  but  the  binding  capacity  of  the  former  is  lower.  In  sand- 
tar  mixtures  containing  a  relatively  large  amount  of  high  carbon  tar,  the 
carbon  may  act  as  a  filler  and  add  to  the  mechanical  strength  of  the  min- 
eral aggregate,  but  better  results  in  this  respect  can  be  obtained  by  the 
use  of  a  smaller  quantity  of  low  carbon  tar  of  the  same  melting  point, 
together  with  a  mineral  filler.  The  waterproofing  value  of  high-carbon 
tars  is  in  general  less  than  that  of  low-carbon  tars.  Free  carbon  retards 
the  absorption  of  tars  by  porous  surfaces.  When  tar  is  exposed  in 
comparatively  thin  films  free  carbon  has  little  or  no  effect  in  retarding 
volatilization. 

Applying  these  facts  to  the  use  of  tar  in  road  treatment  the  following 
conclusions  are  logically  deduced:  (1)  In  the  treatment  of  old  road 
surfaces  a  low  carbon  tar  is  to  be  greatly  preferred  to  a  high  carbon  tar. 
(2)  In  ordinary  bituminous  road  construction,  both  from  the  standpoint 
of  efficiency  and  economy,  a  low-carbon  tar  is  to  be  preferred  to  a  high- 
carbon  tar  whose  bitumen  content  is  of  the  same  consistency. 

The  distillation  test  of  tars  furnishes  information  regarding 
their  utility  for  road  work.  Formerly  the  test  was  made  on  ma- 
terial which  might  or  might  not  contain  water,  but  the  tend- 
ency of  specialists  at  present  is  to  remove  any  water  from  the 
samples  by  preliminary  distillation  at  a  low  temperature,  for  no 
water  is  permitted  in  tar  for  hot  application  under  most  speci- 
fications now.  The  distillation  is  carried  on  in  an  Engler  flask 
and  is  conducted  in  a  series  of  stages.  The  terminal  tempera- 
tures of  the  stages  have  usually  been  110°C.,  170°C.,  270°C.  and 
300°C.,  but  recently  it  has  been  proposed  to  make  another  stage 
with  a  terminal  temperature  of  235°C.  The  test  is  one  which  must 
be  conducted  with  careful  observance  of  the  procedure  speci- 
fied for  the  method  followed  or  the  results  will  not  be  comparable. 
The  distillate  obtained  during  each  stage  is  called  a  *  'fraction." 

The  1916  requirements  of  several  State  highway  departments 
for  different  grades  of  tar  are  given  in  the  table  on  pages  136 
and  137. 


136 


AMERICAN   HIGHWAY  ASSOCIATION 


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At  60°C. 
Residue  after  carrying  distillation  to  315°C. 
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r  This  tar  may  contain  not  over  1  per  cent  of  water. 
5  First  50  cc.  at  50°C.  ;  specific  viscosity. 
1  The  distillate  to  110°C.  must  not  exceed  2  per  cent. 
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BITUMINOUS  ROADS1 

Bituminous  materials  are  used  on  gravel  and  broken  stone  roads 
in  three  ways:  (1)  thoroughly  mixed  with  the  stone  or  gravel 
before  the  latter  is  placed  on  the  roads;  (2)  driven  into  the 
interstices  between  the  stone  after  the  latter  has  been  placed  on 
the  road;  (3)  applied  to  the  surface  of  a  finished  gravel  or  broken 
stone  road.  The  first  method  produces  what  is  now  commonly 
called  bituminous  concrete  and  the  second  method  bituminous 
macadam.  These  will  be  described  in  this  section  and  surface 
applications  will  be  described  in  the  next  section. 

Rock  for  Bituminous  Roads.2 — In  bituminous  road  work  obser- 
vations indicate  that  in  some  cases  it  is  advantageous  to  use  a 
rock  of  relatively  high  absorption  rather  than  one  with  low 
absorptive  qualities,  owing  to  a  better  adhesion  of  the  bituminous 
material  by  a  partial  surface  impregnation  of  the  rock. 

While  the  binding  or  cementing  value  of  a  rock  is  a  most 
important  consideration  from  the  standpoint  of  ordinary  macadam 
construction,  the  same  is  not  true  of  broken-stone  roads  which 
are  carpeted  or  constructed  with  an  adhesive  bituminous  material. 
The  French  coefficient  of  wear  is  also  of  relatively  less  importance, 
owing  to  the  fact  that  the  fine  mineral  particles  produced  by  the 
abrasion  of  traffic  combine,  or  should  combine,  with  the  bitumi- 
nous material  to  form  a  mastic  which  is  held  in  place  and  pro- 
tects the  underlying  rock  from  abrasion  so  long  as  it  is  kept 
intact  by  proper  maintenance.  The  toughness  of  the  rock  is  of 
more  importance,  as  the  shock  of  impact  is  to  a  considerable 
extent  transmitted  through  the  seal  coat  and  may  cause  the 
underlying  fragments  to  shatter.  It  would,  therefore,  seem  that 
the  minimum  toughness  of  a  rock  for  use  in  the  construction  of 
a  bituminous  broken-stone  road  or  a  broken-stone  road  with  a 

1  It  is  the  purpose  of  this  chapter  to  indicate  the  methods  followed  in 
several  sections  of  the  country  where  bituminous  roads  have  been  built 
extensively  rather  than  to  recommend  any  methods  as  the  best  for  all 
conditions.    Revised  by  P.  St.  J.  Wilson,  chief  engineer,  United  States 
Office  of  Public  Roads  and  Rural  Engineering;  F.  H.  Joyner,  road  com- 
missioner of  Los  Angeles  County,  Cal.;  and  W.  R.  Farrington,  division 
engineer,  Massachusetts  Highway  Commission. 

2  From  Bulletin  370,  United  States  Department  of  Agriculture,  "Physi- 
cal Tests  of  Road-Building  Rock,"  by  Prevost  Hubbard,  chemical  engi- 
neer,  and  Frank  H.  Jackson,  Jr.,  assistant  testing  engineer,  OfHce  of 
Public  Roads. 

138 


BITUMINOUS   ROADS  139 

bituminous-rnat  surface  should,  for  light  traffic,  be  no  less  than 
for  ordinary  macadam  subjected  to  the  same  class  of  traffic. 
For  moderate  and  heavy  traffic,  however,  the  same  minimum 
toughness  should  prove  sufficient,  owing  to  the  cushioning  effect 
of  the  bituminous  matrix.  No  maximum  limit  of  toughness  need 
be  considered  for  any  traffic. 

In  the  case  of  bituminous  concrete  roads,  where  the  broken 
stone  and  bituminous  material  are  mixed  prior  to  laying  and 
consolidation,  it  generally  appears  advisable  to  set  a  minimum 
toughness  of  6  to  7  for  light-traffic  roads,  instead  of  5,  in  order  to 
insure  that  the  fragments  of  rock  which  have  been  coated  with 
bitumen  shall  not  be  fractured  under  the  roller  during  consolida- 
tion; and  12  or  13  for  moderate  and  heavy  traffic,  instead  of  10 
and  19,  as  in  the  case  of  water-bound  macadam  roads. 

Bearing  in  mind  the  fact  that  availability,  cost,  and  various 
local  conditions  generally  control  the  selection  of  proper  limits, 
the  accompanying  table  may  be  used  as  a  general  guide  for 
minimum  limits  of  the  French  coefficient  of  wear  and  toughness 
in  connection  with  bituminous  broken-stone  roads. 

Bituminous  Materials. — Climatic  conditions,  the  volume  and 
character  of  traffic  to  be  carried  by  a  road,  the  kind  of  stone  to 
be  used,  and  the  methods  of  construction  vary  greatly  in  differ- 
ent places  and  have  an  important  influence  on  the  determination 
of  the  bituminous  materials  to  be  used.  For  this  reason  it  is  not 
practicable  to  have  a  general  specification  of  universal  applica- 
bility. The  requirements  for  bituminous  binders  of  a  number 
of  states  are  given  in  the  tables  on  pages  126,  127  and  136. 

In  most  cases  the  binders  are  furnished  by  the  contractors 
under  specifications  of  greater  or  less  detail.  In  Massachusetts 
the  State  highway  commission  usually  purchases  its  material  and 
furnishes  it  to  the  contractors,  although  contractors  are  occa- 
sionally required  to  supply  it. 

Bituminous  Macadam. — Roads  of  this  type  are  frequently  said 
to  be  built  by  the  "penetration"  method  because  the  bituminous 
material  is  made  to  penetrate  the  interstices  of  the  road  from  the 
surface.  The  grading,  drainage  and  rolling  of  the  subgrade  are 
carried  out  as  in  the  case  of  waterbound  macadam  roads.  On  the 
subgrade  is  laid  a  base  or  bottom  course,  then  a  top  course  to 
which  the  bituminous  material  is  applied,  and  finally  a  thin 
"seal"  coat  of  bituminous  material  covered  with  screenings  or 
gravel  to  protect  the  main  mass  of  the  road  from  the  weather 
and  other  deteriorating  influences. 

The  depth  of  the  bottom  course  varies  with  the  character  of 
the  subgrade,  the  traffic,  the  quality  of  the  stone,  the  character 
of  the  top  course  and  the  preferences  of  the  highway  authorities. 
Probably  6  inches  at  the  center  and  4  inches  at  the  sides  are 


140 


AMERICAN   HIGHWAY  ASSOCIATION 


Limits  of  Physical  Tests  of  Rock  for  Bituminous  Roads 
(Recommended  by  Pr6vost  Hubbard  and  Frank  H.  Jackson,  Jr.) 


LIGHT  TO  MODERATE  TRAVEL 

MODERATE  TO   HEAVY  TRAVEL 

French 
coefficient 

Percent- 
age of  wear 

Toughness 

French 
coefficient 

Percent- 
age of  wear 

Toughness 

Broken  stone  with 
bituminous  car- 
pet 

At  least 

5 

5 

7 

Not  over 

8 
8 

5.7 

At  least 
5 

5 

7 

At  least 

7 

7 
10 

Not  over 

5.7 

5.7 
4 

At  least 

10 

10 
13 

Bituminous  macadam 
with  seal  coat 

Bituminous  concrete  . 

Gallons  of  Bituminous  Material  per  Mile  of  Road  for  Different  Rates  of 

Application 


GALLONS 
PER 
SQUARE 
YARD 

WIDTH  OF  ROAD  IN  FEET 

9 

10 

12 

15 

18 

20 

22 

0.20 

1,056 

1,174 

1,408 

1,760 

2,112 

2,347 

2,582 

0.25 

1,320 

1,467 

1,760 

2,200 

2,640 

2,933 

3,227 

0.33 

1,742 

1,936 

2,323 

2,904 

3,484 

3,872 

4,259 

0.40 

2,112 

2,347 

2,816 

3,520 

4,224 

4,694 

5,163 

0.50 

2,640 

2,934 

3,520 

4,400 

5,280 

5,867 

6,454 

0.60 

3,168 

3,520 

4,224 

5,280 

6,336 

7,040 

7,744 

0.67 

3,538 

3,931 

4,716 

5,896 

7,075 

7,862 

8,648 

0.70 

3,696 

4,107 

4,928 

6,160 

7,392 

8,214 

9,035 

0.75 

3,960 

4,400 

5,280 

6,600 

7,920 

8,801 

9,680 

0.80 

4,224 

4,694 

5,632 

7,040 

8,448 

9,387 

10,326 

0.90 

4,752 

5,280 

6,336 

7,920 

9,494 

10,561 

11,616 

1.00 

5,280 

5,867 

7,040 

8,800 

10,560 

11,734 

12,907 

1.25 

6,600 

7,334 

8,800 

11,000 

13,200 

14,668 

16,134 

1.50 

7,920 

8,801 

10,560 

13,200 

15,840 

17,601 

19,361 

1.75 

9,240 

10,267 

12,320 

15,400 

18,480 

20,535 

22,587 

2.00 

10,560 

11,734 

14,080 

17,600 

21,120 

23,468 

25,814 

average  depths.1  In  Massachusetts,  where  the  foundation  is  pre- 
pared very  carefully,  sometimes  consisting  of  12  inches  or  more 
of  gravel  or  telford,  an  18-foot  roadway  usually  has  a  bottom 
course  2  inches  thick  at  the  sides  and  3  inches  thick  at  the  center, 
after  rolling,  except  on  stone  foundations,  where  the  standard 
thickness  is  2  inches  at  all  points  of  the  cross-section.  These 
thicknesses  are  increased  in  some  cases. 

The  Massachusetts  specifications  call  for  smaller  stone  than 
those  of  most  states,  and  give  the  engineer  the  final  decision 


1  On  roads  where  the  traffic  promises  to  be  heavy,  it  is  often  considered 
best  to  have  the  same  depth  the  entire  width  of  the  road. 


BITUMINOUS   ROADS  141 

regarding  the  proportions  of  the  J  to  IJ-inch  size  and  the  1J  to 
2J-inch  size  which  shall  be  mixed  together  for  this  course,  the 
intention  being,  where  stone  is  crushed  locally,  to  vary  these 
proportions  in  order  to  use  the  output  of  the  crusher.  In  New 
York  and  Pennsylvania  the  maximum  size  of  the  stone  for  this 
course  is  3|  inches.  The  Pennsylvania  specifications  require  the 
stone  to  have  a  French  coefficient  of  wear  of  not  less  than  10, 
and  permit  the  use  of  gravel  and  of  broken  slag  which  weighs  70 
pounds  or  more  per  cubic  foot,  measured  loose.  In  Ohio,  if  sand- 
stone is  used  in  the  bottom  course,  pieces  as  large  as  6  inches  are 
permitted;  the  maximum  size  with  other  rocks  is  4  inches.  In 
Illinois  and  California  the  maximum  size  is  3  inches.  These 
variations  are  due  mainly  to  differences  in  the  average  quality 
of  stone  available  in  the  different  states. 

After  the  stone  has  been  spread,  it  is  sometimes  harrowed.  The 
Illinois  specifications  call  for  the  use  of  a  tooth  harrow  weighing 
10  to  12  pounds  per  tooth.  The  course  is  then  consolidated  with 
a  roller,  one  weighing  10  tons  or  more  being  generally  required. 
It  is  next  covered  with  screenings,  small  gravel  and  sometimes 
coarse  sand,  which  are  broomed  and  rolled  dry  until  the  inter- 
stices are  filled,  but  not  over-filled.  Some  engineers  consider  the 
course  finished  at  this  stage,  while  others  require  it  to  be  sprinkled 
with  water  and  rolled  so  as  to  consolidate  it  still  further. 

On  the  work  under  a  number  of  State  highway  departments, 
the  stone  for  both  the  top  and  bottom  courses  must  be  shoveled 
from  the  carts  into  place,  or  be  dumped  on  platforms  and  shoveled 
from  there  into  place,  or  be  spread  over  the  road  by  distributing 
wagons  built  for  the  purpose.  In  other  states  the  stone  for  the 
bottom  course  may  be  dumped  on  the  subgrade  and  shoveled 
from  these  piles  into  its  final  place.  Stone  for  the  top  course  is 
never  permitted  to  be  dumped  in  piles  on  the  bottom  course. 
The  screenings  or  other  fine  material  used  on  the  road  are  gen- 
erally required  to  be  delivered  along  the  road  before  construction 
begins. 

Other  types  of  bottom  courses  than  those  made  of  graded 
aggregates  are  occasionally  used.  Many  macadam  roads  in  good 
condition  have  had  a  bituminous  macadam  top  course  put  on 
them.  Macadam  roads  when  in  poor  condition  are  often  scari- 
fied, new  material  added  where  needed,  and  then  rolled,  thus 
furnishing  a  suitable  bottom  course  at  minimum  expense.  If 
these  old  roadways  are  thus  used,  their  drainage  should  be  care- 
fully examined  and  all  defects  remedied  before  the  top  course  is 
laid.  In  the  New  York  state  highways,  a  base  of  run-of-bank 
gravel  not  larger  than  3J  inches  is  sometimes  used.  In  this  case 
the  material  passing  a  J-inch  screen  must  not  be  more  than  5  per 
cent  in  excess  of  the  voids  in  the  remainder  of  the  material  after 
this  fine  stuff  has  been  removed. 


142  AMERICAN   HIGHWAY   ASSOCIATION 

In  Massachusetts  the  top  course  is  usually  2  inches  thick,  and 
as  stone  from  1J  to  2^  is  required  the  largest  pieces  become  im- 
bedded slightly  in  the  bottom  course  by  the  rolling.  More  than 
15  per  cent  of  the  J  to  If -inch  stone,  which  is  permitted  in  the 
bottom  course,  is  not  desired  in  the  top  course  because  experi- 
ence has  convinced  the  Massachusetts  engineers  that  its  presence 
makes  a  less  durable  road.  More  bituminous  binder  is  required 
with  coarse  than  small  stone,  but  the  entire  quantity  can  be 
applied  at  one  time,  while  if  small  stone  is  used  it  has  been 
found  desirable  to  construct  this  course  in  two  layers  in  order  to 
be  certain  that  the  smaller  voids  existing  with  such  stone  are 
filled. 

The  top  course  in  most  States  is  usually  from  2  to  3  inches 
thick. 

The  top  course  of  the  New  York  State  highways  is  made  of  1J 
to  2J  inches  stone,  in  Pennsylvania  1  to  3-inch,  in  Ohio  If  to  1\- 
inch  stone  for  a  course  less  than  3  inches  thick  and  2J  to  4-inch 
stone  for  a  course  3  inches  or  more  thick,  unless  the  stone  has  a 
loss  on  abrasion  of  less  than  6  per  cent,  when  the  size  is  reduced 
to  2  to  3f  inches;  in  Illinois  1  to  2i  inches.  The  Ohio  and 
Illinois  specifications  require  it  to  be  harrowed. 

In  rolling  this  course,  it  is  usually  considered  desirable  to  roll 
adjacent  strips  of  the  shoulders  as  well,  so  as  to  unite  the  shoulder 
and  roadway  as  completely  as  practicable.  It  is  also  generally 
considered  desirable  to  roll  the  stone  until  it  is  "locked"  in  place 
so  the  binder  distributor  can  pass  without  leaving  any  impres- 
sion, but  not  to  the  maximum  density.  The  reason  for  this  is 
that  the  bituminous  material  is  believed  to  be  more  uniformly 
distributed  if  the  course  of  stone  is  capable  of  further  compression 
after  the  binder  has  been  applied.  Some  stone  hard  enough  to 
carry  travel  should  not  be  rolled  heavily,  for  if  heavily  rolled  the 
voids  will  be  so  reduced  that  the  binder  will  not  penetrate  into 
them  properly. 

No  bituminous  material  should  be  applied  except  when  the 
stone  on  the  surface  is  clean  and  free  from  dust.  The  applica- 
tion is  now  made  in  many  cases  with  a  pressure  distributor, 
which  is  required  by  some  State  highway  departments;  it  is  also 
applied  by  gravity  distributors  and,  on  small  work,  by  hand 
pouring  cans. 

Distributing  wagons  often  have  some  kind  of  fire-box  for  keep- 
ing the  binder  hot.  Gravity  distributors  discharge  their  contents 
through  nozzles  or  other  spraying  devices  at  their  rear  about  12 
inches  above  the  road.  The  shape  and  location  of  the  nozzles 
are  so  selected  that  the  binder  will  be  distributed  uniformly 
over  a  strip  of  the  road  somewhat  wider  than  the  distance  be- 
tween the  wheels.  The  binder  flows  from  the  nozzles  by  gravity, 


BITUMINOUS   ROADS  143 

and  as  the  contents  of  the  tank  are  drawn  off  the  pressure  on  the 
nozzles  decreases  and  the  rate  of  flow  per  minute  is  reduced. 
In  order  to  maintain  a  uniform  flow,  a  control  valve  in  the  out- 
let pipe  is  provided.  The  rate  of  application  of  the  material  is 
regulated  by  this  valve  and  the  speed  of  the  distributor. 

Pressure  distributors  are  used  where  it  is  desired  to  have  better 
control  over  the  rate  of  application  of  the  binder  than  is  practic- 
able with  gravity  distributors,  and  also  to  obtain  the  best  dis- 
tribution and  penetration.  In  some  types,  compressed  air  or 
steam  is  admitted  to  the  top  of  the  tank  so  that  the  pressure  on 
the  surface  of  the  binder,  whether  the  tank  is  full  or  almost  empty, 
is  sufficient  to  drive  the  material  through  the  nozzles  with  con- 
siderable force.  In  other  types,  the  binder  is  driven  out  of  the 
nozzles  by  a  small  pump.  The  nozzles  of  the  pressure  distrib- 
utors are  generally  about  6  inches  from  the  surface  of  the  road. 
In  some  cases  the  binder  is  forced  through  a  hose  ending  in  a 
nozzle  which  the  operator  moves  along  just  above  the  surface  of 
the  road. 

Bituminous  material  is  also  distributed  from  tank  wagons  with- 
out any  suitable  piping  and  nozzles  of  their  own.  This  is  done 
by  attaching  to  their  rear  end  a  light  two-wheel  sulky  having  the 
necessary  distributing  apparatus,  which  is  connected  by  piping 
with  the  outlet  of  the  tank  wagon.  Attachments  are  also  made 
for  this  purpose  which  can  be  bolted  to  an  ordinary  tank  wagon. 

Pouring  cans  resemble  garden  watering  cans  in  appearance. 
The  top  is  usually  partly  covered  to  prevent  the  binder  from  slop- 
ping out,  and  there  is  generally  a  removable  screen  which  intercepts 
anything  likely  to  clog  the  nozzle.  The  nozzle  is  a  slot  6  to  10 
inches  long,  which  is  usually  adjustable.  A  skillful  man  can 
apply  bituminous  material  in  this  way  very  uniformly,  but  the 
expense  on  large  work  is  greater  than  with  distributors. 

The  binder  can  be  heated  in  portable  kettles,  usually  mounted 
on  wheels,  in  distributing  wagons,  oil  heating  pits,  or  in  tank  cars, 
the  method  to  be  followed  depending  upon  the  amount  of  material 
to  be  heated. 

The  amount  of  binder  used  is  from  li  to  If  gallons  per  square 
yard,  depending  upon  the  depth  and  size  of  the  stone.  If  an 
asphalt  binder  is  used  it  must  be  applied  at  a  temperature  of 
about  300°F.  and  if  tar  at  about  200°  to  225°F.  After  it  is  spread 
it  is  covered  with  small  stone,  usually  from  about  i  to  f  inches 
in  size;  in  New  York  State  work  stone  of  f  to  li  inches  is  speci- 
fied. In  Massachusetts  good  results  have  been  obtained  in 
some  cases  with  sand.  After  this  dressing  has  been  spread  it  is 
often  gone  over  with  brooms  to  make  certain  that  all  voids  in  the 
surface  are  filled,  and  the  material  unformly  distributed,  and  the 
brooming  should  be  finished  with  the  brooms  working  parallel  with 
the  line  of  the  road. 


144  AMERICAN   HIGHWAY  ASSOCIATION 

After  the  top  course  has  become  firm  under  the  roller,  the 
surface  is  swept  clean  and  the  seal  coat  is  applied.  This  is  usually 
spread  at  the  rate  of  J  to  }  gallon  per  square  yard,  and  is  covered 
with  i  to  f-inch  stone  chips  or  pea  gravel.  The  road  is  then 
broomed,  using  a  lock  street  broom  for  the  purpose,  and  then 
given  a  thorough  rolling  as  to  consolidate  it  as  much  as  possible 
and  the  broom  can  be  attached  to  the  roller  during  this  final  rolling. 
A  liberal  use  of  both  the  hand  broom  and  the  lock  street  broom, 
or  the  broom  fastened  to  the  roller,  during  the  screening  and 
finishing  of  the  road  will  do  much  to  insure  that  the  dressing 
is  evenly  taken  up  by  the  oil  and  a  smooth  riding  surface  obtained 
that  will  not  start  the  pounding  of  automobiles  and  the  con- 
sequent rippling  of  the  surface. 

In  the  State  highway  work  of  Illinois,  there  are  there  courses 
and  a  seal  coat  in  bituminous  macadam  construction.  The  sec- 
ond course  is  1  to  2i-inches  stone,  harrowed,  rolled,  and  treated 
with  1  gallon  of  binder  per  square  yard.  This  is  covered  with  J 
to  J-inch  screenings,  which  are  broomed  into  the  voids  and  the 
excess  swept  off.  A  second  application  of  binder  is  then  made 
at  the  rate  of  \  gallon  per  square  yard  and  covered  with  torpedo 
gravel  ranging  in  size  from  f-inch  down  to  fine  sand.  This  is 
broomed  until  the  voids  are  filled,  when  the  surplus  is  removed. 
Another  application  of  binder  is  made  at  the  rate  of  \  gallon 
per  square  yard  and  covered  with  torpedo  gravel  at  the  rate  of 
about  1  cubic  yard  per  200  square  yards  of  road.  The  wheels 
of  the  roller  may  be  wet  to  prevent  them  from  picking  up  the 
binder;  some  engineers  object  to  such  wetting  and  require  the 
wheels  to  be  oiled. 

Where  the  grade  is  steep,  the  Massachusetts  highway  com- 
mission has  recently  tried  the  practice  of  leaving  the  surface 
rather  rough,  so  as  to  afford  a  foothold  for  horses  and  resistance 
to  skidding  for  automobiles. 

Bituminous  Concrete. — When  the  stone  and  binder  are  mixed 
together  thoroughly  before  they  are  placed  on  the  road,  it  is  prac- 
ticable to  use  both  small  and  large  stone  and  thus  reduce  the  vol- 
ume of  the  voids  to  be  filled  with  bituminous  binder.  This  mate- 
rial is  placed  on  any  of  the  bottom  courses  used  with  bituminous 
macadam  and  also  on  concrete.  It  is  essential  for  the  bottom 
course  to  be  dry  and  clean  when  the  inixture  is  spread  over  it. 

The  size  of  the  stone  required  by  different  State  highway 
departments  varies  somewhat,  and  some  departments  have  a 
number  of  standard  proportions.  In  Massachusetts  crusher- 
run  trap  from  J  to  1J  inches  is  specified  for  some  roads,  and  also 
crushed  gravel,  which  will  be  mentioned  later.  In  New  York, 
f  to  IJ-inch  stone  is  used  for  a  course  2  inches  or  less  in  thick- 
ness, and  for  thicker  courses  stone  up  to  2J  inches  in  size  is 


BITUMINOUS    ROADS  145 

allowed.  In  both  New  York  and  Maryland  materials  are  per- 
mitted which  will  give  a  finished  pavement  with  less  than  10 
per  cent  passing  a  2-mesh  screen,  8  to  22  per  cent  passing  a  4- 
mesh,  25  to  55  per  cent  passing  a  10-mesh,  18  to  30  per  cent 
passing  a  40-mesh,  5  to  11  per  cent  passing  a  200-mesh,  and  7 
to  11  per  cent  of  bitumen.  In  Maryland  a  mixture  is  also  used 
containing  two  parts  of  J  to  11-inch  stone  and  one  part  of  sand 
with  25  per  cent  passing  a  20-mesh  screen  and  5  per  cent  passing 
80-mesh.  To  this  mixture  is  added  5  per  cent  of  powdered  lime- 
stone or  cement  and  7  to  9  per  cent  of  bitumen.  In  Illinois  the 
proportions  are  left  to  the  engineer,  but  the  purpose  is  to  obtain 
the  equivalent  of  a  thorough  mixture  of  1  cubic  yard  of  grit  sand 
passing  a  f-inch  ring  with  40  to  80  per  cent  passing  a  10-mesh 
sieve,  and  3  cubic  yards  of  f  to  l£  inch  stone  with  30  to  80  per 
cent  retained  on  a  1-inch  ring.  Instead  of  the  stone  3  cubic 
yards  of  f  to  1-inch  gravel  with  20  to  70  per  cent  retained  on  a 
f-inch  screen  may  be  used. 

The  amount  of  bituminous  binder  on  the  Massachusetts  work 
is  about  20  to  24  gallons  per  cubic  yard  of  stone.  In  New  York, 
for  the  work  with  broken  stone  without  fine  material,  18  gallons 
are  used  per  cubic  yard  of  stone  and  the  purpose  is  to  have  the 
finished  course  contain  from  5  to  7J  per  cent  by  weight  of  bitumen. 
On  the  Illinois  work,  from  27  to  30  gallons  of  binder  containing 
95  per  cent  or  more  of  bitumen  is  used  per  cubic  yard  of  stone  or 
gravel,  and  if  the  binder  contains  less  than  95  per  cent  of  bitumen 
the  quantity  must  be  increased  proportionately. 

Although  stone  and  tar  binder  have  occasionally  been  mixed 
cold,  as  in  Rhode  Island,  it  is  customary  to  mix  the  stone  and 
bituminous  material  hot.  There  is  a  marked  difference  of  opin- 
ion regarding  the  temperature  to  which  the  stone  should  be  heated, 
Massachusetts  requiring  this  to  be  180°F.  or  more  and  Illinois 
300°  to  375°.  A  high  temperature  will  injure  some  binders  and 
not  others,  and  it  is  therefore  important  to  have  the  aggregate 
uniformly  heated  to  the  proper  temperature  for  the  binder  used, 
the  weather  conditions,  and  the  length  of  haul  from  the  mixing 
plant  to  the  road.  The  binder  is  heated  in  kettles  or  tanks.  The 
temperature  for  asphalt  is  275°  to  375°  and  for  tar  200°  to  275°, 
the  limits  varying  somewhat  with  the  grades  used.  Special  care 
must  be  taken  to  prevent  overheating.  Sometimes  hot  stone  and 
cold  binder  are  mixed.  The  mixing  on  small  work  can  be  done 
by  hand,  but  is  more  quickly  and  thoroughly  performed  on  large 
work  in  mixers  made  for  the  purpose. 

The  best  equipment  for  any  contract  will  depend  upon  local 
conditions,  among  which  the  transportation  of  the  mixed  mate- 
rial is  an  important  factor.  The  mixture  must  be  delivered 
on  the  site  at  temperatures  of  150°  to  280°,  according  to  the 


146  AMERICAN  HIGHWAY  ASSOCIATION 

binder  used.  The  maximum  permissible  drop  between  the  tem- 
peratures of  the  material  at  the  mixer  and  when  it  reaches  the 
road,  freedom  from  segregation  in  the  mixture,  and  the  practi- 
cable speed  of  delivery,  fix  the  maximum  length  of  haul.  If  the 
maximum  length  of  haul  permits  the  use  of  a  central  plant  for 
the  whole  work,  it  is  often  practicable  to  locate  it  at  the  crusher 
plant  and  save  some  labor  charges.  Portable  plants  for  use  along 
the  road  have  been  greatly  improved  in  recent  years  and  are  used 
extensively. 

The  wagons  for  transporting  the  mixture  should  be  tight,  and 
under  some  weather  and  hauling  conditions  their  contents  should 
be  covered  with  canvas  to  keep  them  from  becoming  chilled.  The 
bodies  of  motor  trucks  are  sometimes  jacketed  or  insulated  for 
the  same  purpose. 

The  mixture  should  be  shoveled  from  the  wagons,  or  dumped 
on  wood  or  metal  platforms  from  which  it  can  be  shoveled.  The 
shovels  are  often  heated,  as  are  the  rakes  used  in  spreading  the 
mixture.  It  is  considered  desirable  by  some  engineers  to  pro- 
hibit delivering  hot  mixture  on  the  road  within  one  hour  of 
sunset. 

When  the  edges  of  the  pavement  are  not  protected  by  a  stone 
or  concrete  curb,  the  New  Jersey  highway  department  requires 
the  contractor  to  place  temporary  curbs  of  6  or  8-inch  planks  of 
the  same  thickness  as  the  finished  top  course. 

When  it  is  necessary  to  lay  half  of  the  width  of  a  road  so  as  to 
allow  traffic  on  the  other  half,  the  base  of  the  first  half  is  allowed 
to  project  about  2  feet  beyond  the  center  line  of  the  roadway. 
The  top  course  in  such  cases  ends  only  a  few  inches  beyond  the 
center  line,  for  this  will  insure  all  of  it  resting  on  a  firm  base. 
After  the  second  half  of  the  base  has  been  constructed,  the  inside 
edge  of  the  top  course  already  laid  is  cut  back  vertically  or  nearly 
so  along  a  straight  or  properly  curved  line  so  as  to  obtain  a 
perfect  joint  with  the  second  half  of  this  course. 

After  the  material  has  been  spread,  it  should  be  rolled  imme- 
diately. Sometimes  an  initial  compression  is  given  with  a  3-  to 
6-ton  tandem  roller  and  the  final  compression  with  a  10-ton 
macadam  roller,  but  the  usual  practice  is  to  use  a  7-  to  10-ton 
roller  giving  200  to  300  pounds  per  linear  inch  of  roll.  The 
wheels  may  be  oiled  to  prevent  the  binder  from  sticking  to  them. 
This  rolling  is  continued  until  the  roller  leaves  no  marks  in  pass- 
ing. Any  places  which  can  not  be  reached  by  the  roller  are 
rammed  with  a  hot  iron  tamp. 

The  road  is  often  given  a  seal  coat  at  the  rate  of  J  to  |  gallon 
of  binder  per  square  yard,  which  is  at  once  covered  with  pea 
stone  or  grit.  The  binder  is  often  the  same  material  used  in  the 
bituminous  concrete  but  sometimes  it  is  a  more  fluid  grade. 


BITUMINOUS   ROADS  147 

Some  engineers  require  it  to  be  applied  with  a  squeegee  distributor. 
The  seal  coat  is  rolled  until  it  is  thoroughly  incorporated  with  the 
top  course. 

Mixed  Gravel-Asphalt  Roads. — The  Massachusetts  highway  com- 
mission has  built  a  number  of  roads  with  mixed  gravel-asphalt 
surfaces  on  gravel  and  broken  stone  bases.  The  surfacing  with  a 
gravel  base  is  2J  inches  thick  after  rolling.  The  folio  whig  notes 
from  its  1915  report  describe  the  construction: 

A  road,  18  feet  in  width  with  3-foot  shoulders,  was  built  everywhere, 
the  curves  being  banked  and  widened  to  21  feet.  A  gravel  foundation  was 
put  in  wherever  the  bottom  was  bad,  and  about  4  inches  of  local  crushed 
stone  was  spread  and  well  rolled. 

On  this  was  spread,  as  evenly  as  possible,  about  3  inches  of  a  bitumi- 
nous mixture  made  of  gravel  that  had  been  run  through  the  crusher  and 
sand  or  stone  dust,  mixed  with  a  heavy  asphaltic  product.  The  gravel 
and  sand  and  the  asphalt  were  thoroughly  heated  and  were  mixed  in  a  hot 
mixer,  and  then  carted  onto  the  road  and  spread.  The  surface  was  rolled 
down  to  about  2  inches  in  thickness  when  the  mixture  was  sufficiently  cool 
not  to  crawl  under  the  roller. 

Great  care  is  necessary  to  insure  a  uniform  product,  uniformly  heated, 
mixed  and  spread,  and  that  sufficient  asphalt  is  used  and  no  more  than 
sufficient  to  bind  the  mixture  properly.  The  quantity  of  asphalt  has  to 
vary  somewhat,  according  to  the  amount  of  voids  in  the  mineral  aggre- 
gate. The  variation  is  usually  from  18  to  22  gallons  of  the  hot  asphalt  to 
the  cubic  yard  of  gravel.  When  the  mixture  is  right  it  has  about  the 
consistency  of  brown  sugar  and  compacts  under  the  roller,  though  when  it 
is  first  spread  and  rolled  it  sometimes  has  a  few  hair  cracks  which  the 
traffic  soon  irons  out.  The  asphaltic  product  used  in  this  work  has  a  pene- 
tration of  from  80  to  120  with  a  Dow  penetrometer. 

Sand  and  Oil  Roads. — In  1905  the  Massachusetts  highway 
commission  surfaced  a  road  at  Eastham  by  distributing  hot 
asphaltic  oil  over  the  sand  which  is  practically  the  only  material 
in  the  vicinity,  applying  1J  gallons  to  the  square  yard  in  two 
applications.  The  results  were  so  encouraging  that  more  sand- 
oil  roads  have  been  built  and  the  experience  thus  gained  has 
shown  what  are  the  requirements  for  success.  They  are  now 
built  by  both  the  penetration  or  layer  method  and  by  the  mixing 
method.  They  are  considered  suitable  when  the  traffic  is  mostly 
light  teams  and  automobiles  and  will  not  stand  up  if  used  daily 
by  many  heavily  loaded  teams.  The  average  daily  traffic  in  1915 
on  one  successful  layer  road  was  20  heavy  teams,  17  light  teams 
and  253  automobiles.  On  a  mixed  road  it  was  6  heavy  teams, 
23  light  teams  and  505  automobiles;  on  another  mixed  road  21 
heavy  teams,  38  light  teams  and  197  automobiles. 

It  is  desirable  for  success  to  use  a  hard,  strong,  sharp  and  well- 
graded  sand,  such  as  is  abundant  on  Cape  Cod,  where  this  type 
of  construction  has  been  developed.  Many  sands  are  too  fine, 
too  uniform  in  size,  too  rounded  or  not  strong  enough.  Fair 
results  have  been  obtained  with  some  fine  sands,  however. 


148  AMERICAN    HIGHWAY    ASSOCIATION 

An  oil  asphalt  of  good  quality  that  will  bind  and  not  lubricate 
must  be  used.  For  the  layer  type,  the  preference  in  Massa- 
chusetts is  for  an  oil  with  a  viscosity  of  150  to  200  seconds  at 
200°C.,  using  a  Lawrence  viscosimeter  or  about  1038  to  1384 
with  100  cc.  at  100°C.  in  an  Engler  viscosimeter.  From  1J  to 
2  gallons  per  square  yard  are  used,  in  two  applications,  with  a 
covering  of  sand  after  application.  In  the  mixed  type,  oil  as- 
phalts having  a  penetration  of  60  to  135  by  the  Dow  penetrometer 
have  been  tried,  but  that  now  used  ordinarily  has  a  penetration 
of  90  to  125.  From  16  to  22  gallons  per  cubic  yard  of  sand  have 
been  used;  the  present  average  is  18  gallons.  The  Massachusetts 
commission  advises  testing  each  carload  of  oil  before  using  it. 

In  the  layer  type  of  construction,  the  commission  spreads  clay 
or  loam  over  the  sand  subgrade  to  reduce  the  rutting  of  the  sur- 
face by  wheels  and  pitting  by  horses'  hoofs  when  the  oil  cart  passes 
over  it.  The  oil  is  then  spread  evenly  while  hot  with  a  dis- 
tributing cart  and  immediately  covered  with  sand.  This  process 
is  then  repeated. 

In  the  mixed  type  of  construction  the  sand  and  oil  are  mixed 
hot  to  form  a  mastic  which  is  spread  over  the  sandy  subgrade 
and  rolled.  The  subgrade  is  carefully  shaped  and  hardened  as 
in  the  case  of  the  penetration  type.  The  mastic  sheet  is  about 
4  inches  thick  at  the  center  and  3  inches  at  the  edges.  The  best 
results  have  been  obtained  by  keeping  the  road  constantly  shaped 
with  a  road  scraper  during  rolling,  and  a  seal  coat  of  J  gallon  of 
a  lighter  oil  such  as  is  used  in  layer  work  improves  the  surface 
and  decreases  maintenance  charges.  In  the  early  work  the  sand 
was  heated  on  sheets  of  iron,  but  this  overheated  parts  of  it  and 
underheated  other  parts,  so  that  now  the  heating  is  done  in  rotary 
heaters. 

If  the  traffic  in  the  future  proves  too  heavy  for  these  roads,  the 
commission  believes  they  can  be  greatly  improved  and  strength- 
ened at  a  moderate  cost  by  using  harder  asphalt,  greater  care  in 
grading  the  sand,  and  the  addition  of  cement  and  stone  dust. 
In  this  way  a  sheet  asphalt  pavement  2  inches  thick  can  be  laid 
on  the  old  sand-asphalt  road  as  a  base. 

Asphalt  Blocks  on  Country  Roads 

As  designed  and  manufactured  for  use  on  country  roads,  the 
asphalt  blocks  are  5  inches  wide,  12  inches  long,  and  2  inches  deep, 
weigh  about  eleven  pounds  each,  and  have  a  specific  gravity  of 
about  2.40. 

The  asphalt  block  was  developed  and  perfected  on  the  theory 
that  crushed  trap  rock,  on  account  of  its  preeminent  hardness  and 
inherent  grittiness,  made  the  best  known  material  for  a  roadway 


BITUMINOUS  ROADS  149 

surface,  the  one  thing  needed  being  a  cement,  or  binding  material, 
to  keep  all  of  the  particles  permanently  in  place.  This  was  accom- 
plished by  the  use  of  an  asphaltic  cement  to  bind  together  the  prop- 
erly graded  particles  of  crushed  trap,  the  hot  mixture  being  con- 
solidated by  tremendous  pressure  into  blocks  so  dense  and  free  from 
voids  as  to  be  practically  non-absorbent.  In  the  asphalt  block, 
therefore,  we  have  an  asphaltic  concrete,  or  macadam,  mixed,  in 
exact  proportions,  at  a  central  plant,  under  conditions  insur- 
ing absolute  uniformity,  and  receiving  the  compression  necessary 
to  produce  a  dense  and  non-absorbent  material. 

Not  only  has  a  special  block  been  produced,  but  a  special  method 
of  construction  has  been  worked  out,  designed  to  utilize  what  is 
left  of  the  worn  and  rutted  macadam  road  as  a  foundation  for  the 
blocks.  This  is  accomplished  by  scarifying  the  surface,  if  necessary, 
filling  up  the  deep  ruts,  rolling  with  a  heavy  steam  roller,  and  lay- 
ing upon  the  surface  of  the  old  macadam,  a  bed  of  cement  mortar 
about  1  inch  in  thickness,  to  serve  the  double  purpose  of  forming 
a  firm  unyielding  bed  for  the  blocks,  and  binding  them  securely 
to  the  macadam  foundation  underneath.  By  this  method  the 
material  used  in  the  original  construction  of  the  road  is  not  thrown 
away,  but  used  as  foundation  for  a  permanent  wearing  surface. 
Where  the  old  macadam  is  too  thin,  or  too  badly  worn  to  be  safely 
used  as  a  foundation,  it  will  be  necessary  to  lay  a  concrete  base, 
but  usually  there  is  broken  stone  enough  in  the  old  macadam  to 
supply  what  is  needed  for  laying  concrete. 

A  pavement  may  be  laid  of  any  desired  width,  contour,  grade, 
or  crown.  It  is  perfectly  feasible  to  pave  one-half  of  the  roadway, 
or  only  a  narrow  strip  in  the  center,  and  extend  the  paved  area 
at  a  later  date  as  traffic  necessities  require,  or  as  appropriations 
become  available.  It  is  not  necessary  to  set  curbstones  or  head- 
ing stones  to  border  or  define  the 
paved  area,  since  a  row  of  stretcher 
blocks  held  firmly  in  place  by  a  shoulder 
of  mortar,  as  shown  in  the  sketch, 
answers  the  purpose  perfectly  and 
leaves  the  entire  roadway  surface 
smooth  and  uniform. 

A  good  example  of  this  construc- 
tion is  on  the  Albany  Post  Road,  through  the  villages  of  Hast- 
ings-on-Hudson,  Dobbs  Ferry,  Irvington,  North  Tarry  town,  Town 
of  Mount  Pleasant,  Briar  cliff  and  Ossining,  N.  Y.,  on  the  Boston 
Post  Road  in  Pelham  Manor  and  Rye,  N.  Y.,  on  9  miles  of  road- 
way from  Daytona  to  Deland,  Volusia  County,  Florida,  and  on 
Nassau  Street,  Princetown,  N.  J.,  a  section  of  the  Lincoln  Highway. 


BITUMINOUS  SURFACE  APPLICATIONS1 

Surface  applications  vary  widely  in  character,  according  to 
their  purpose.  In  most  cases  such  an  application  is  essentially  a 
maintenance  measure,  but  in  the  case  of  the  bituminous  mats  or 
wearing  courses  used  in  California,  or  the  mats  now  laid  on  new 
water-bound  macadam,  the  first  cost  of  such  work  is  essentially 
a  part  of  the  first  cost  of  the  improvement.  The  practice  in 
making  such  surface  applications  of  any  general  type  varies 
widely  in  different  parts  of  the  country,  more  widely  than  the 
practice  in  any  other  branch  of  road  work.  Whether  greater 
uniformity  will  prove  desirable  or  the  work  can  be  done  success- 
fully by  a  wide  variety  of  methods  can  not  be  definitely  deter- 
mined until  the  records  of  such  work  and  of  the  traffic  on  roads 
are  kept  with  more  detail  and  uniformity  than  at  present.  The 
widespread  interest  in  the  subject  was  one  of  the  leading  charac- 
teristics of  highway  affairs  in  1916,  and  was  an  evidence  of  the 
conditions  mentioned. 

Oiling  Earth  Roads 

Surface  applications  on  earth  roads  were  made  in  California 
many  years  ago,  and  a  method  of  incorporating  oil  and  earth  by 
a  special  form  of  roller  was  employed  for  some  time.  More 
recently  well  built  earth  roads  in  Iowa  and  Illinois  have  received 
surface  applications  as  a  maintenance  measure.  The  experience 
in  these  states  shows  that  while  some  success  follows  applications 
on  roads  that  are  not  in  good  condition,  it  is  very  desirable  to 
have  the  surface  properly  shaped  and  hard  before  the  oil  is  applied. 
The  oil  binds  the  grains  of  earth  together  and  reduces  the  dust, 
but  it  does  not  give  the  resistance  to  attrition  which  a  hard  sur- 
face affords.  The  treatment  is  therefore  one  which  must  be 
regarded  as  adapted  only  for  roads  with  light  traffic  and  light 
vehicles.  If  sand  instead  of  earth  is  present,  the  methods  of  con- 
struction first  used  in  Massachusetts  and  described  on  page  147 
should  be  considered. 

If  the  road  has  ruts  and  holes  in  the  surface  and  is  poorly 
drained,  water  will  collect  in  puddles,  soften  the  oiled  crust  at 

1  Revised  by  George  H.  Biles,  second  deputy  State  highway  commissioner 
of  Pennsylvania,  and  B.  H,  Piepmeier,  maintenance  engineer  of  the  Illinois 
State  highway  department. 

150 


BITUMINOUS   SURFACE   APPLICATIONS  151 

these  places,  and  seep  into  the  roadbed.  The  material  under  the 
crust  will  give  way  under  heavy  loads  and  the  money  spent  in 
oiling  will  be  largely  lost,  because  the  oiled  material  will  become 
mixed  with  the  unoiled  material  below  and  dust  will  be  produced 
about  as  freely  as  on  an  unoiled  road.  Furthermore,  the  oiling 
of  a  mudhole  often  aggravates  troubles  due  to  such  a  defect. 

The  surface  to  receive  the  application  must  be  dry,  or  the  oil 
will  not  penetrate  the  pores,  and  it  must  be  free  from  dust,  for 
the  oil  forms  flakes  or  scales  with  the  dust  and  these  are  a  worse 
nuisance  than  plain  dust,  being  very  irritating  to  the  eyes. 

Both  cold  and  hot  applications  have  been  used  successfully  in 
Iowa,  but  the  State  Highway  Commission  prefers  to  heat  the  oil 
as  it  apparently  gives  enough  better  penetration  to  justify  the 
additional  expense.  It  is  desirable  to  secure  the  advice  of  a 
specialist  in  selecting  the  oil.  A  light  oil  must  be  used  and  as 
it  may  have  a  low  flash  point,  care  should  be  taken  to  keep  it  at 
a  temperature  below  its  flash  point  and  to  prevent  any  of  it 
coming  into  contact  with  a  flame.  The  first  application  is  made 
at  a  rate  of  about  J  gallon  per  square  yard,  and  later  applications 
at  the  rate  of  J  to  |  gallon.  The  brief  experience  in  such  work 
indicates  that  two  light  applications  annually  for  two  years  and 
afterward  a  single  application  annually  will  be  sufficient  on  a 
road  adapted  for  such  treatment  and  not  subject  to  traffic  requir- 
ing a  more  durable  surface.  During  1916  the  Illinois  State  high- 
way department  issued  the  following  advice  on  the  work. 

The  best  results  may  be  secured  during  the  first  application,  by  apply- 
ing either  a  cold  oil  or  at  least  a  very  thin  product  that  will  penetrate  the 
surface  of  the  road  several  inches  and  at  the  same  time  contain  as  many 
binding  elements  as  possible  so  as  to  seal  all  pores  in  the  earth,  making  it 
waterproof  and  at  the  same  time  adding  some  binding  qualities  that  may 
assist  the  bond  of  the  soil  itself.  A  suitable  product,  as  is  commonly 
expressed,  may  vary  from  30  to  60  per  cent  in  asphalt.  After  the  surface 
of  the  road  has  been  thoroughly  saturated,  a  hot  oil  or  a  slightly  heavier 
product  may  be  used. 

If  the  heavier  oils  are  used  for  the  first  application  they  will  not  readily 
penetrate  the  surface  of  the  road  and  will  consequently  form  a  mat  on 
top.  The  forming  of  the  mat  before  the  surface  of  the  road  is  more  or  less 
waterproof  may  be  a  serious  fault  as  moisture  will  accumulate  beneath  the 
mat  and  the  road  will  be  much  slower  in  drying  out  than  it  would  had  the 
oil  not  been  applied.  The  mat  surface  with  a  soft  subsoil  will  rut  more 
readily,  besides  breaking  and  scaling  off  in  large  pieces,  making  the  road 
surface  rough  and  undesirable. 

The  Illinois  authorities  recommend  covering  the  oiled  surface 
with  clean,  hard  sand,  at  the  rate  of  a  cubic  yard  to  100  to  150 
square  yards. 


152  AMERICAN   HIGHWAY   ASSOCIATION 

Broken  Stone  Road  Surfacing 

It  has  been  found  that  a  surface  application  on  a  new  water- 
bound  macadam  road  may  prove  unsatisfactory,  although  if  the 
road  is  exposed  to  traffic  for  three  months  the  desired  results  are 
obtained  if  the  treatment  is  properly  carried  out.  This  is  prob- 
ably due  to  the  large  amount  of  fine,  lightly-bound  dust  on  the 
roadway,  which  is  removed  by  the  early  traffic,  or  to  the  greater 
stability  of  the  road  as  a  result  of  its  consolidation  by  traffic. 
In  New  York,  macadam  roads  finished  so  late  in  the  fall  that  they 
can  not  have  three  months  wear  before  winter,  are  given  a  surface 
application  of  calcium  chloride  as  a  temporary  protection  against 
raveling  during  the  months  that  must  elapse  before  bituminous 
surfacing  can  be  placed. 

In  making  thin  surface  applications  to  an  old  road  that  is  thick 
enough  to  carry  the  prospective  traffic  and  has  a  surface  in  fair 
condition,  the  ruts  and  holes  must  first  be  patched.  This  is  best 
done  several  days  in  advance  of  the  surfacing.  Each  hole  or 
rut  is  swept  clean,1  painted  with  bituminous  material  and  filled 
with  J  to  1?  inch  stone  and  binder.  The  stone  and  binder  are 
often  mixed  at  a  central  point  and  carted  along  the  road  by  the 
patching  gang,  for  use  where  required.  Just  before  the  surfacing 
is  done,  the  road  is  swept  thoroughly,  often  with  some  type  of 
revolving  broom.  Sometimes  wire  brooms  are  used  first  and  then 
fiber  brooms.  The  oil  is  applied  hot  or  cold  according  to  quality 
at  the  rate  of  about  J  to  f  gallon  per  square  yard,  as  the  engi- 
neer considers  best,  and  then  covered  with  clean  screenings,  granu- 
lated slag  or  gravel  at  the  rate  of  about  60  pounds  per  square 
yard.  It  is  advisable  to  secure  the  advice  of  a  specialist  in 
selecting  the  oil.  The  oil  is  applied  by  hand  on  small  work,  but 
usually  with  a  distributor.  If  the  screenings  are  distributed  by 
hand  they  should  be  previously  deposited  in  piles  at  convenient 
intervals  along  the  roadside.  They  are  also  distributed  by 
spreader  carts.  The  length  of  time  the  road  should  be  closed  to 
traffic  depends  upon  the  weather,  character  of  the  oil,  and  the 
amount  of  screenings  used,  varying  from  1  to  48  hours. 

If  the  road  oil  rises  through  the  screenings,  or  " bleeds,"  in  hot 
weather,  more  screenings  should  be  spread  over  those  places.  If 
the  road  is  used  mainly  by  automobiles,  a  thin  covering  of  screen- 
ings is  sometimes  spread  first  and  later  a  covering  of  sand  or  other 
fine  material,  to  act  as  a  filler  and  prevent  the  tires  from  dislodging 
the  screenings. 

The  following  rules  for  the  amount  of  bituminous  material  to 
be  used  in  surfacing  broken  stone  roads  were  prepared  by  George 
H.  Biles,  second  deputy  highway  commissioner  of  Pennsylvania: 

1  It  is  desirable  to  cut  the  edges  of  a  hole  so  as  to  secure  vertical  faces 
to  which  the  new  material  will  adhere  properly;  a  patch  with  a  feather  edge 
is  liable  to  be  unsatisfactory. 


BITUMINOUS   SURFACE   APPLICATIONS  153 

If  the  surface  of  the  road  is  made  up  of  pieces  of  ballast  size  stone 
(3-inch)  from  which  traffic  has  removed  all  the  fine  material,  leaving  large 
surface  voids  between  the  stone,  enough  of  the  bituminous  material  must 
be  applied  so  that  it  will  flush  up  level  to  the  top  of  the  large  pieces  of  stone 
and  firmly  bind  the  chips  and  gravel  which  lie  in  the  crevices  between  the 
stone. 

If,  on  the  other  hand,  the  surface  of  the  road  is  equally  clean,  but  traffic 
has  not  removed  the  fine  particles  between  these  stones  to  the  same  extent, 
and  the  crevices  between  them  are  consequently  smaller,  then  a  somewhat 
smaller  amount  of  bituminous  material  should  be  used,  since  an  excess 
will  again  flow  off  the  road. 

In  treating  a  road  which  has  recently  been  resurfaced,  it  will  be  found 
often  that  even  after  all  the  screenings  and  fine  material  have  been  swept 
from  the  top  of  the  road  leaving  the  large  stones  bare,  there  will  still  be  a 
certain  amount  of  dust  and  fine  material  between  the  stones  which  has 
not  yet  been  compacted  thoroughly  by  traffic  and  which  will  absorb  the 
bituminous  material  like  a  blotter,  leaving  only  a  brown  stain  in  these 
spaces.  In  such  cases,  the  amount  of  application  must  be  increased  until 
this  fine  material  is  well  saturated  and  there  is  enough  of  the  bituminous 
material  near  the  surface  of  the  road  to  bind  thoroughly  the  covering  of 
chips  or  gravel. 

The  first  application  of  a  bituminous  surfacing  to  a  waterbound 
macadam  road  may  be  disappointing.  The  hoofs  of  horses  are 
liable  to  dislodge  the  mat  and  the  surface  will  have  a  spotted 
appearance.  After  several  applications,  however,  the  macadam 
surface  will  become  protected  everywhere. 

On  the  New  York  State  highways  which  are  thick  enough  to 
carry  the  traffic  but  are  too  rough  to  be  treated  satisfactorily  with 
cold  oil  and  screenings,  surfacing  with  two  applications  of  hot 
oil  is  sometimes  done.  After  the  old  road  is  patched  and  cleaned, 
it  is  covered  with  0.4  to  0.6  gallon  of  oil  to  the  square  yard,  over 
which  just  enough  1-inch  stone  is  spread  to  cover  the  surface. 
This  is  rolled  lightly  and  then  covered  with  0.3  to  0.4  gallon  of 
oil  per  yard.  This  is  covered  with  \  inch  stone  in  the  thinnest 
possible  layer,  which  is  rolled  as  soon  as  the  oil  is  cool  enough  to 
permit  it. 

On  the  Illinois  highways,  when  a  double  application  is  made, 
about  }  gallon  per  square  yard  is  used  on  each  application,  and 
the  preferred  covering  is  torpedo  sand,  \  to  f  inch  in  size,  but 
clean,  stone  chips  are  also  employed.  The  total  amount  of  cover- 
ing material  with  such  a  treatment  is  one  cubic  yard  for  each  125 
square  yards  of  road.  When  a  single  application  is  made  \  to 
J  gallon  of  oil  per  square  yard  and  a  cubic  yard  of  torpedo  sand 
for  every  150  square  yards  of  road  are  employed. 

Bituminous  sandstone  obtained  in  Kentucky  has  been  used  in 
parts  of  that  state  for  re-surfacing  old  macadam.  The  latter  is 
scarified,  smoothed  with  a  road  machine,  and  enough  new  stone 
added  to  give  the  desired  thickness  and  contour.  This  is  rolled 
thoroughly  and  then  covered  with  pulverized  bituminous  sand- 


154  AMERICAN   HIGHWAY   ASSOCIATION 

stone  to  a  depth  of  about  If  inches,  loose,  when  spread.  It  is 
desirable  to  allow  the  sun  to  shine  on  the  loose  material  for  a  few 
hours,  until  it  appears  slightly  oily,  and  then  roll  it,  slowly  at 
first  and  later  more  rapidly. 

Concrete  Road  Surfacing 

While  surface  applications  to  concrete  roads  have  been  em- 
ployed in  a  number  of  states,  there  is  no  agreement  as  to  their 
desirability.  They  have  been  used  to  the  greatest  extent  in 
California,  where  both  thin  wearing  surfaces  and  an  asphaltic 
mixture  are  used.  The  following  information  concerning  both 
types  was  supplied  by  Austin  D.  Fletcher,  State  highway  engineer 
of  California. 

The  thin  bituminous  wearing  surface  is  about  half  an  inch  in  thickness 
when  completed.  After  it  has  been  under  traffic  for  a  few  months  it  is 
found  to  contain  a  fairly  uniform  mixture  of  mineral  aggregate  and  bitumi- 
nous binder  consisting  of  about  8  to  11  per  cent  of  bitumen  and  the  balance 
mineral  aggregate  of  a  fairly  uniform  grading  running  from  dust  to  rock 
of  ^-inch  maximum  diameter.  It  shows  no  tendency  to  flow  or  creep  and 
the  surface  remains  true  and  free  from  rolling.  The  concrete  base,  how- 
ever, must  be  finished  with  a  true,  smooth  surface  to  make  a  good  riding 
highway  as  this  type  of  surfacing  is  not  thick  enough  to  smooth  up  to  any 
considerable  extent  a  concrete  pavement  whose  surface  is  uneven. 

The  procedure  in  laying  this  thin  wearing  surface  is  as  follows:  First 
the  surface  of  concrete  is  cleaned  of  dirt,  dust  films  and  any  thin  coat  of 
laitance.  This  is  best  accomplished  by  opening  the  bare  concrete  to 
traffic  for  a  month  or  two.  The  iron  shod  traffic  and  the  rapidly  moving 
rubber  tires  are  of  greatest  help  in  breaking  any  weak  layers  of  dirt  or 
laitance  and  exposing  the  surface  of  the  concrete  proper.  This  "traffic 
cleaning"  is  followed  by  brushing  with  revolving  street  brooms  and  hand 
brooms.  In  some  cases  flushing  the  surface  with  water  is  a  help  in  wash- 
ing off  any  thin  coat  of  clay.  It  is  of  greatest  importance  that  the  asphaltic 
oil  bind  to  the  solid  concrete  and  not  to  any  overlving  weak  film  of  dirt. 
The  care  taken  in  getting  a  clean  concrete  is  without  doubt  in  a  large 
measure  responsible  for  the  success  of  this  surfacing  because  of  the  strength 
of  the  bond  between  the  concrete  and  the  bituminous  wearing  coat.  The 
few  failures  where  the  wearing  surface  has  been  stripped  from  the  con- 
crete have  been  nearly  always  easy  to  trace  to  a  pavement  improperly 
cleaned  prior  to  the  application  of  the  road  oil. 

After  the  concrete  has  been  cleaned  the  asphaltic  oil  is  applied  by  a 
pressure  distributor  at  the  rate  of  J  gallon  per  square  yard.  This  oil 
surface  is  immediately  covered  by  a  layer  of  either  crushed  rock  screenings 
or  fine  gravel  of  \  to  £  inch.  This  material  may  contain  some  fines  and 
dust  but  should  be  fairly  clean. 

The  screenings  are  applied  by  shoveling  from  piles  placed  at  frequent 
intervals  alongside  the  road.  The  shovelers  can  be  taught  to  so  throw 
the  screenings  that  they  will  cover  the  road  surface  with  a  fairly  uniform 
thickness.  The  road  can  now  with  advantage  be  given  a  light  rolling  but 
this  is  not  necessary.  Any  excess  screenings  should  be  swept  into  piles 
alongside  of  the  road  to  be  used  on  the  second  application  of  road  oil.  This 
is  applied  on  the  second  application  at  the  same  rate  and  is  covered  with 
screenings  as  before. 


BITUMINOUS   SURFACE   APPLICATION  155 

The  road  is  now  thrown  open  to  traffic  and  during  the  first  two  weeks 
may  require  further  screenings  to  take  up  excess  oil.  The  traffic  is  of  great 
assistance  in  forcing  the  screenings  into  the  oil  and  compacting  and  mak- 
ing a  homogeneous  carpet  on  the  concrete. 

The  oil  is  applied  to  the  road  at  a  temperature  of  from  250°  to  300°. 
It  contains  approximately  90  per  cent  of  80°  penetration  asphalt.  In 
California  the  road  oil  companies  classify  this  product  as  a  "90-80"  road 
oil. 

In  building  the  thin  bituminous  wearing  surface  for  concrete  pavements 
two  physical  properties  of  the  road  oil  are  of  greatest  importance.  First 
the  oil  must  be  of  such  a  viscosity  that  when  applied  to  the  road  it  will 
readily  combine  with  the  screenings  that  are  thrown  upon  its  surface. 
A  very  viscous  oil  will  form  a  hard  surface  and  the  screenings  will  lie 
there  without  being  absorbed  and  to  a  large  extent  be  thrown  off  the  road 
by  the  passing  traffic.  Only  a  small  amount  will  settle  or  be  forced  into 
the  oil  and  the  surface  will  not  build  up  into  a  satisfactory  protecting 
wearing  coat. 

The  second  physical  property  of  great  importance  is  that  the  road  oil 
must  be  cementing  or  adhesive  so  that  it  will  bind  tightly  to  the  concrete 
surface  and  bind  together  all  of  the  fragments  of  stone  screenings.  It 
should  be  an  active  cement  and  if  it  is  not  sticky  then  the  wearing  sur- 
face will  not  be  firm  enough  to  resist  the  push  and  pull  of  the  passing 
traffic. 

The  State  highway  routes  leading  from  the  great  centers  of  population 
have  required  a  higher  type  of  surfacing  to  meet  successfully  the  demands 
of  heavy  traffic. 

After  proper  curing  of  the  concrete  its  surface  is  cleaned  of  all  dirt  and 
dust  films  and  given  a  paint  binder  coat  composed  of  asphaltic  cement 
and  engine  distillate  of  lightest  gravity.  The  asphalt  used  has  a  penetra- 
tion between  80°  and  90°,  the  mix  being  one  part  asphalt  and  one  to  two 
parts  distillate,  the  exact  proportion  of  distillate  being  determined  by 
trial.  The  satisfactory  mixture  is  one  that  paints  the  concrete  with  a  thin, 
uniform,  glossy  black  film  which  becomes  hard  two  hours  after  application. 

The  surfacing  used  has  the  following  composition  expressed  in  per- 
centages : 

Bitumen  soluble  in  carbon  disulphide,  7^—10 

Aggregate: 

PASSING  REFUSING 

200  sieve         8-13  per  cent. 


80 

40 

10 

4 

2 


200  sieve  14-25  " 

80       "  17-29  " 

40       "  5-11  " 

10       "  15-25  " 

4       "  3-10  " 


100 


The  asphaltic  cement  used  has  a  penetration  of  from  70  to  90  degrees, 
District  of  Columbia  standard,  and  passes  the  usual  requirements  for 
solubility,  volatility  and  ductility.  The  heating  of  asphalt,  aggregates 
and  dust  and  mixing  and  laying  follow  the  usual  practice. 

Prior  to  the  laying  of  the  surfacing,  the  testing  laboratory  makes  grad- 
ing tests  of  such  sand,  limestone  dust  and  rock  screenings  as  will  be  avail- 
able for  the  work  and  selects  such  of  these  that  give  the  desired  mix.  In 
this  selection  the  following  points  are  considered  important: 

Let  a  be  taken  as  the  percentage  of  asphaltic  cement  that  will  be  used 
in  the  finished  material.  Then  the  dust  passing  the  200-mesh  sieve  should 
at  least  equal  a-1.  The  fine  sand  passing  the  80  mesh  and  retained  on 


156  BITUMINOUS   SURFACE   APPLICATIONS 

the  200  should  be  approximately  2a.  If  the  available  sand  is  high  on  the 
finer  sieves  a  may  be  taken  as  high  as  9.5  per  cent.  If  the  sand  is  coarse, 
a  may  be  as  low  as  8  per  cent  for  the  trial  mix.  The  coarse  aggregate  pass- 
ing the  No.  2  sieve  and  retained  on  No.  10  should  be  from  28  to  35  per  cent 
of  the  other  mix.  If  these  points  are  satisfied  by  the  available  material 
the  weights  of  coarse  aggregate,  fine  aggregate,  dust  and  asphaltic  cement 
can  be  given  to  the  road  crew  for  a  trial  batch.  Under  field  working  con- 
ditions a  trial  batch  will  show  if  the  mix  is  "wet"  or  "dry"  and  by  a  slight 
change  in  the  percentage  of  asphaltic  cement  a  mixture  can  be  made  that 
will  rake  and  roll  properly.  In  this  way  the  mineral  aggregate  is  not 
changed  but  kept  under  known  satisfactory  grading.  As  the  work  pro- 
ceeds, grading  tests  should  be  run  at  frequent  intervals  on  the  different 
mineral  aggregates  to  insure  a  uniform  grading  in  the  finished  pavement. 
Analysis  of  samples  of  the  different  batches  should  also  be  made  to  check 
the  uniformity  of  the  mix. 

The  surface  after  thorough  rolling  should  have  a  specific  gravity  in 
excess  of  2.20  if  the  sands  and  crushed  rock  screenings  are  of  average  spe- 
cific gravities.  A  sample  of  the  finished  pavement  taken  each  day  and 
tested  for  specific  gravity  will  indicate  if  there  has  been  insufficient  com- 
pression, either  due  to  method  of  rolling  or  to  the  surface  being  too  cold 
when  rolled. 


BRICK  ROADS1 

Brick  pavements  have  been  used  on  the  streets  of  American 
cities  for  many  years  and  the  United  States  Bureau  of  the  Census 
reports  that  in  1909  they  formed  nearly  24  per  cent  of  the  entire  mile- 
age of  paved  streets  in  158  cities.  Some  of  the  early  brick  pave- 
ments gave  satisfactory  service  for  many  years,  but  others  did 
not.  The  unsatisfactory  early  experience  was  due  in  part  to 
the  use  of  unsuitable  materials,  in  part  to  the  improper  recon- 
struction of  pavements  cut  to  permit  laying  pipes,  and  in  part 
to  the  defective  methods  of  construction  employed,  just  as  was 
the  experience  with  other  types  of  block  pavements.  It  is  not 
possible  to  build  lasting  block  pavements  unless  the  blocks  are 
prevented  from  settling,  which  results  in  holes  in  the  surface, 
or  from  tilting  over  on  their  bottom  side,  called  "turtling," 
which  results  in  a  rounding  of  the  upper  edges  of  the  blocks, 
called  "cobbling."  These  defects  led  to  better  methods  of 
construction,  so  that  when  bricks  came  into  use  on  country 
highways  success  was  assured  if  municipal  experience  was  taken 
as  a  guide.  There  are  always  communities  as  well  as  persons 
unwilling  to  profit  by  the  experience  of  others,  however,  and  con- 
sequently some  brick  roads  have  been  built  of  poor  materials 
and  by  poor  methods  with  the  inevitable  unsatisfactory  results. 
Such  unfortunate  experience  was  unnecessary  then  and  is  un- 
necessary today;  it  was  largely  due  to  ignorance  of  the  require- 
ments for  good  work,  carelessness,  lack  of  proper  supervision, 
and  a  desire  to  cheapen  the  cost  of  such  roads  below  the  amount 
needed  for  proper  construction. 

Paving  Bricks 

Paving  bricks  are  made  from  a  great  variety  of  shales  and  fire 
clays  and  consequently  bricks  of  equal  worth  vary  considerably 
in  appearance.  Shale  contains  iron  which  makes  shale  bricks 
red  when  burned  under  normal  oxidizing  conditions  and  brown 

1  Revised  by  William  W.  Marr,  chief  state  highway  engineer  of  Illinois; 
A.  H.  Hinkle,  deputy  highway  commissioner  of  Ohio;  P.  M.  Tebbs,  engi- 
neer of  construction  of  the  Pennsylvania  State  Highway  Pepartment; 
Will  P.  Blair,  secretary  of  the  National  Association  of  Paving  Brick  Manu- 
facturers; and  W.  C.  Perkins,  chief  engineer,  R.  T.  Stull,  ceramic  engi- 
neer, and  F.  A.  Churchill,  of  the  Dunn  Wire-Cut  Lug  Brick  Company. 

157 


158  AMERICAN   HIGHWAY   ASSOCIATION 

or  nearly  black  when  burned  under  reducing  conditions.  Fire 
clays  have  less  iron  than  shales,  the  iron  being  present  in  a  com- 
bined state,  and  bricks  made  from  them  are  buff-colored,  unless 
reducing  conditions  during  burning  darken  them.  The  shales 
and  fire  clays  are  often  unsuited  for  making  paying  bricks  as  they 
occur,  and  then  material  from  one  stratum  in  a  pit  must  be 
mixed  with  that  from  another  stratum  or  that  from  one  pit  with 
that  from  another,  and  sometimes  with  sand  or  surface  clay. 

The  raw  materials  are  crushed  and  ground  dry  in  large  revolv- 
ing pans  under  heavy  rolls,  called  "mullers."  This  material  is 
screened  to  remove  pieces  of  too  large  size,  and  is  then  conveyed 
to  a  pug  mill,  in  which  the  materials  are  mixed  somewhat  as 
concrete  is  mixed  in  a  continuous  concrete  mixer.  Here  enough 
water  is  added  to  convert  the  material  into  a  thick  mud,  which 
is  beaten  by  the  revolving  blades  into  a  condition  of  uniform 
consistency  and  composition.  This  mud  is  fed  continuously 
into  a  brick  machine,  where  it  is  forced  by  an  auger  through  a 
die,  whence  it  emerges  as  a  fairly  hard  bar  of  rectangular  section, 
which  is  cut  mechanically  into  bricks.  This  bar  of  hard  clay  may 
be  approximately  4  by  4?  inches  in  section,  in  which  case  it  is 
cut  about  every  9  inches,  forming  "end-cut"  bricks,  or  it  may  be 
approximately  9  by  4$  inches  in  section  and  cut  every  4  inches, 
forming  "  side-cut"  bricks.  These  bricks  are  sometimes  sub- 
mitted to  a  reshaping  process  before  drying,  in  which  case  they 
are  called  "re-pressed"  bricks,  and  sometimes  they  are  dried  as 
they  are  finished  by  the  brick  machine,  in  which  case  they  are 
called  "wire-cut"  bricks.  For  drying,  the  bricks  are  placed  on 
cars  which  are  run  very  slowly  through  a  long,  tunnel-like  heater, 
into  which  hot  dry  air  is  admitted  continuously.  After  remain- 
ing on  the  cars  in  the  tunnel  about  twenty-four  hours  their 
weight  is  reduced  from  15  to  20  per  cent.  The  bricks  are  then 
ready  for  burning,  one  of  the  most  important  steps  in  the  manu- 
facturing process.  The  bricks  are  stacked  in  kilns  in  such  a 
way  that  the  heated  air  circulates  freely  around  them,  and  great 
care  must  be  taken  in  the  regulation  of  the  temperature  through- 
out the  entire  burning  process,  from  the  time  the  kiln  is  first 
warmed  until  it  is  cool  enough  to  permit  the  withdrawal  of  the 
bricks. 

In  laying  paving  bricks  a  space  is  left  between  successive  rows 
for  the  material  which  forms  the  joints,  and  as  it  is  very  desir- 
able for  these  joints  to  be  of  a  uniform  width,  one  side  of  a  paving 
brick  has  either  two  or  four  lugs,  which  are  small  projections 
from  the  surface  of  the  bricks.1  These  projections  serve  to  keep 

1  There  are  some  bricks  which  do  not  have  lugs  but  have  raised  letters 
or  four  projections,  one  near  each  corner,  on  one  face.  Raised  letters  are 
not  permitted  on  bricks  for  Ohio  State  roads. 


BKICK   ROADS  159 

the  adjacent  faces  the  proper  distance  apart  when  the  bricks  are 
forced  into  contact  during  the  paving  operations.  These  pro- 
jections extend  J  to  J  inch  from  the  side  or  face.  In  one  class  of 
side-cut  bricks  the  cutting  is  done  by  wires  which  are  moved 
across  the  bar  of  clay  so  as  to  produce  the  lugs  needed  on  one  side 
of  the  brick.  These  are  called  "wire-cut  lug"  bricks.  In  an- 
other type  of  side-cut  bricks,  2J,  3  and  4  inches  deep,  the  ribs 
are  moulded  on  one  of  the  sides  as  it  comes  through  the  die.  A 
wire-cut  side  is  placed  on  top  in  laying  such  bricks,  which  are 
called  "vertical  fiber"  bricks  in  some  parts  of  the  country.  Other 
types  of  projections  are  made  by  devices  attached  to  the  brick 
machine.  In  the  case  of  repressed  bricks,  the  projections  from 
one  or  both  sides  are  made  in  the  press. 

There  is  no  universal  standard  size  for  bricks  but  the  tendency 
seems  to  be  toward  3J  inches  width,  4  inches  depth  and  8^  inches 
length,  with  a  permissible  variation  of  f  inch  either  way  in  the 
width  and  depth  and  i  inch  either  way  in  length.  The  depth  is 
occasionally  reduced  as  much  as  an  inch  for  roads  having  light 
traffic,  when  the  monolithic  and  cement-sand  cushion  types  of 
construction,  explained  later,  are  used. 

"Hillside"  bricks  are  made  for  use  on  grades  of  5  per  cent  or 
more.  They  have  one  or  more  grooves  cut  the  full  length  of  the 
bricks,  along  their  edges,  in  the  case  of  bricks  to  be  laid  in  the 
usual  manner,  or  two  grooves  cut  transversely  in  the  case  of  bricks 
to  be  laid  parallel  with  the  curb.  These  grooves  are  about  f  inch 
deep  and  are  intended  to  prevent  slipping  of  horses  or  automo- 
biles. Bricks  with  beveled  edges  are  used  for  grades,  notably  on 
the  carriage  ramps  of  the  Pennsylvania  Terminal  in  New  York, 
where  the  travel  is  very  heavy,  and  quite  generally  on  grades  ex- 
ceeding 5  per  cent,  throughout  Ohio. 

Tests  of  Bricks 

The  color  of  the  interior  of  bricks  from  the  same  plant  gives 
an  indication  of  their  quality,  for  generally  the  color  is  darker 
in  the  bricks  burned  with  the  higher  temperatures.  The  color  of 
the  exterior  of  the  bricks  is  a  less  reliable  indication  of  quality, 
and  even  interior  color  is  of  little  or  no  value  in  judging  the  bricks 
from  different  plants.  The  other  features  of  bricks  which  can 
be  determined  by  visual  inspection  are  explained  in  the  follow- 
ing description  of  the  bricks  which  may  be  rejected  under  the 
standard  specifications  of  the  American  Society  for  Testing 
Materials : 


160  AMERICAN   HIGHWAY  ASSOCIATION 

All  bricks  which  are  broken  in  two  or  chipped  in  such  a  manner  that 
neither  wearing  surface  remains  substantially  intact,  or  that  the  lower  or 
bearing  surface  is  reduced  in  area  by  more  than  one-fifth.1 

All  bricks  which  are  cracked  in  such  a  degree  as  to  produce  defects  such 
as  are  defined  in  (the  previous  paragraph)  either  from  shocks  received  in 
shipment  and  handling,  or  from  defective  conditions  of  manufacture, 
especially  in  drying,  burning  or  cooling,  unless  such  cracks  are  plainly 
superficial  and  not  such  as  to  perceptibly  weaken  the  resistance  of  the  brick 
to  its  condition  of  use. 

All  bricks  which  are  so  off-size,  or  so  misshapen,  bent,  twisted  or  kiln- 
marked,  that  they  will  not  form  a  proper  surface  as  defined  by  the  paving 
upecifications,  or  align  with  other  bricks  without  making  joints  other  than 
those  permitted  in  the  paving  specifications. 

All  bricks  which  are  obviously  soft5  and  too  poorly  vitrified  to  endure 
street  wear. 

Formerly  a  number  of  different  laboratory  tests  of  the  properties 
of  paying  bricks  were  required  by  specifications,  but  today  reli- 
ance is  placed  mainly  on  the  rattler  test  to  determine  their  qual- 
ity. Its  name  is  derived  from  the  use  of  a  foundry  rattler,  em- 
ployed in  cleaning  iron  castings,  in  making  the  first  tests  of  this 
kind  on  bricks.  The  rattler  used  today  is  constructed  specially 
for  the  purpose.  It  is  an  iron  and  steel  barrel  of  the  cross-section 
of  a  14-sided  polygon,  about  20  inches  long  and  28  inches  in  diam- 
eter, inside  dimensions,  with  a  shaft  projecting  from  each  end. 
This  barrel  is  mounted  in  a  frame  with  the  shafts  horizontal  and 
can  be  revolved  by  power. 

Ten  dry  bricks  are  weighed  and  placed  within  the  rattler, 
together  with  an  abrasive  charge  consisting  of  10  cast-iron  spheres 
weighing  from  7  to  7J  pounds  each  and  a  sufficient  number  of 
cast-iron  spheres  from  If  to  1J  inches  in  diameter  and  weighing 
from  0.75  to  0.95  pound  each,  to  make  a  total  charge  of  300 
pounds.  The  rattler  is  then  revolved  1800  times  at  the  rate  of 
29^  revolutions  per  minute.  In  this  way  the  bricks  are  sub- 
jected to  innumerable  blows  which  are  considered  to  imitate  the 
conditions  of  service  more  nearly  than  any  other  test  yet  de- 

1  Mr.  Tebbs  makes  this  comment:  "The  area  of  a  standard  brick  is  about 
30  square  inches  and  I  consider  about  one-fifth  or  6  square  inches  a  very 
large  allowance.  I  think  that  a  reduction  of  not  more  than  one-tenth  of 
the  area  should  be  permitted."  This  comment  is  not  approved  by  Mr. 
Blair  on  the  grounds  that  experience  has  shown  no  ill  effects  from  the  rule 
of  the  Society,  and  to  limit  the  reduction  of  area  to  10  per  cent,  would  in- 
crease materially  the  cost  of  the  bricks. 

a  Mr.  Tebbs  advises  adding  the  words,  "not  uniformly  vitrified,  badly 
laminated."  The  phrasing  of  the  standard  specifications  was  debated  at 
great  length  before  adoption,  and  uniform  vitrification  was  not  adopted 
as  a  requirement  because  no  brick  is  uniformly  vitrified,  strictly  speak- 
ing. The  words  "badly  laminated"  are  sometimes  used,  but  objection 
has  been  raised  to  them  as  not  conveying  to  the  inspector  the  meaning  of 
the  engineer,  which  is  to  reject  bricks  having  laminations  that  are  separate 
one  from  the  other,  sometimes  called  "open"  laminations. 


BBICK  ROADS 


161 


vised.  When  the  test  is  finished,  the  bricks  are  taken  out,  all 
pieces  of  them  weighing  less  than  1  pound  are  discarded,  and  the 
remainder  are  weighed.  The  loss  in  weight  during  the  test, 
expressed  as  a  percentage  of  the  original  weight,  is  the  form  in 
which  the  results  are  stated. 

The  percentage  of  permissible  loss  in  the  rattler  test  is  fixed 
at  different  amounts  in  order  to  meet  the  conditions  imposed  by 
differences  in  travel  and  the  experience  of  different  localities  with 
bricks  of  various  grades.  The  American  Society  for  Testing 
Materials  gives  the  following  scales  of  maximum  permissible 
losses  for  different  classes  of  travel : 


CHARACTER   OF  TRAVEL 

MAXIMUM  PER 

MIS8IBLE   LOSS 

Average 

Single  brick 

Heavy  

22 

24 

24 

26 

Light  

26 

28 

The  New  York  and  Pennsylvania  State  highway  departments' 
specifications  call  for  the  medium-travel  grade  and  Ohio  and 
Illinois  for  the  heavy-travel  grade.  In  Illinois  the  wire-cut 
lug  bricks  are  given  1  per  cent  higher  permissible  loss  than  the 
repressed  bricks,  which  must  conform  to  the  tabulated  require- 
ments. In  that  State  there  is  a  minimum  permissible  loss  spec- 
ified, 17  per  cent  for  wire-cut  and  16  per  cent  for  repressed  bricks. 
The  average  permissible  maximum  loss  may  reach  25  per  cent 
for  wire-cut  lug  bricks  if  no  individual  brick  loses  more  than 
28  or  less  than  20  per  cent,  and  may  reach  27  per  cent  if  the 
range  of  loss  of  every  individual  brick  is  between  29  and  23  per 
cent.  With  repressed  bricks,  the  average  loss  may  reach  24 
per  cent,  with  a  range  of  27  to  19  per  cent  for  every  individual 
brick,  and  26  per  cent  with  a  range  of  28  to  22  per  cent.  These 
requirements  put  a  premium  on  uniformity  in  the  bricks,  which 
many  engineers  regard  as  of  importance  in  preventing  unequal 
wear  of  the  surface  of  a  brick  road.  They  hold  that  where  soft 
and  hard  bricks  are  laid  together  indiscriminately,  some  of  the 
bricks  are  worn  away  more  rapidly  than  where  a  pavement  is 
laid  with  bricks  of  a  more  uniform  quality. 

In  New  York  and  Ohio  30  bricks  form  a  lot  for  sampling. 
These  represent  the  hard,  medium  and  light-burned  bricks  de- 
livered on  the  job,  and  each  grade  is  tested  separately.  During 
testing  there  is  a  large  percentage  of  failures  in  the  abrasion  test, 
partially  caused  by  the  selection  of  light  and  hard-burned  brick. 
The  laboratory  results  obtained  on  such  bricks  serve  as  a  guide 
in  throwing  out  or  culling  part  of  the  bricks  on  the  job. 


162  AMERICAN   HIGHWAY   ASSOCIATION 

Some  years  ago  the  crushing  strength  and  specific  gravity  of 
paving  bricks  were  considered  properties  which  should  be  speci- 
fied, but  experience  has  shown  that  it  is  unnecessary  to  do  so. 
The  specific  gravity  of  fire-clay  bricks  averages  between  2.1  and 
2.25  and  that  of  shale  bricks  between  2.2  and  2.4.  The  crushing 
strength  of  good  paving  bricks  ranges  from  10,000  to  20,000 
pounds  per  square  inch,  when  the  test  load  is  applied  over  the 
entire  top  surface  of  the  specimens,  and  may  be  higher  if  only  a 
part  of  the  surface  is  loaded.  This  is  from  five  to  ten  times  the 
probable  maximum  load  on  a  pavement. 

The  capacity  of  a  brick  to  absorb  water  was  formerly  consid- 
ered an  important  indication  of  its  porosity,  and  low  porosity 
was  held  to  be  essential  for  strength  and  good  sanitary  proper- 
ties, which  were  then  considered  as  particular  advantages  of 
brick  pavements.  With  the  improvements  that  have  been  made 
in  the  rattler  test  and  the  increased  knowledge  of  the  slight  in- 
fluence of  a  wide  range  in  porosity  upon  the  sanitary  value  of 
such  pavements,  the  absorption  test  has  lost  much  of  its  former 
favor  among  roadbuilders.  It  affords  useful  information  in 
comparing  bricks  made  under  identical  conditions  and  for  other 
research  work,  and  it  is  still  required  by  a  few  State  highway 
departments.  In  Ohio,  the  bricks  taken  from  a  rattler  after 
testing  in  that  apparatus  must  not  absorb  more  than  3J  per  cent 
of  their  weight  of  water  during  immersion  for  forty-eight  hours. 
In  Pennsylvania,  the  absorption  of  thoroughly  dried  bricks  im- 
mersed in  water  for  twenty-four  hours  must  not  exceed  3J  per 
cent. 

Another  test,  formerly  used  extensively,  probably  because  the 
apparatus  for  making  it  was  available  in  many  schools  and  easily 
obtained,  is  the  transverse  or  cross-breaking  test.  It  is  now 
little  used  outside  of  New  York  and  New  Jersey.  In  the  former 
State  the  test  required  by  the  highway  department  is  to  place 
the  sample  brick  on  edge  on  two  parallel  supports  6  inches  apart 
and  load  it  at  the  center  until  it  breaks.  If  the  distance  in 
inches  between  the  supports  is  represented  by  L,  the  load  in 
pounds  which  produces  rupture  by  W,  and  the  width  and  depth 
in  inches  of  the  brick  by  b  and  d  respectively,  the  modulus  of 
rupture  will  be  3WL/2bd2,  which  must  not  be  less  than  2000 
pounds  in  bricks  for  New  York  state  work. 

Curbs 

Curbs  are  required  along  the  sides  and  ends  of  brick  pave- 
ments laid  on  a  sand  cushion  or  laid  on  natural  soil  and  having 
sand-filled  joints,  in  order  to  hold  the  bricks  at  those  places  and 
also,  with  some  types  of  base,  to  hold  the  material  of  the  base  in 


BKICK  ROADS  163 

place.  Planks  have  been  used,  but  their  short  life  compared  with 
that  of  the  pavement  makes  them  undesirable,  for  nobody  can 
foretell  whether  they  will  be  renewed  as  they  wear  out.  In 
some  places  stone  slabs  can  be  obtained  for  the  purpose  at  prices 
which  enable  them  to  be  used  economically.  Vitrified  curbs  are 
sometimes  used,  but  require  more  careful  bedding  than  stone 
curbs,  because  their  shorter  length  and  lighter  weight  render 
them  more  subject  to  displacement.  Concrete  is  most  gener- 
ally used  for  curbs.  In  country  highway  work  the  top  of  the 
curb  is  usually  flush  with  the  surface  of  the  pavement.  If  a  con- 
crete base  is  used,  the  curb  is  usually  an  integral  part  of  it,  and 
is  generally  from  6  to  8  inches  wide  on  top.  If  a  concrete  base 
is  not  used,  the  depth  of  the  curb  must  be  governed  mainly  by 
the  character  of  the  subgrade,  the  frost  hazard  and  the  character 
of  the  shoulders.  In  any  case  it  is  desirable  to  have  the  top  2 
inches  of  the  concrete  curb  not  leaner  than  a  1:2:3  mixture, 
finished  with  a  wooden  float,  and  the  outer  surface  should  be 
spaded.  This  spading  is  done  by  placing  a  spade  in  the  form 
against  the  outer  plank  and  rocking  it  back  and  forth  so  as  to 
force  the  coarse  aggregate  of  the  fresh  concrete  away  from  the 
face. 

Where  the  bricks  are  bedded  on  mortar  or  green  concrete, 
most  engineers  believe  that  curbs  are  not  needed.1  If  they  are 
omitted  special  care  must  be  given  to  providing  firm  shoulders 
along  the  marginal  bricks. 

The  Base 

A  brick  pavement  requires  an  absolutely  firm  unyielding  sup- 
port. Ail  old  macadam  road  thoroughly  underdrained  and  se- 
cure against  settlement  or  upheaval  ,is  considered  a  satisfactory 
support  by  some  engineers.  But  it  is  rarely  possible  to  find  such 
a  road,  for  usually  the  drainage  is  defective,  the  cross-section  has 
too  much  crown,  or  the  grades  are  wrong.  It  is  then  necessary 
to  disturb  the  hard  crust  of  the  road  and  this  is  very  likely  to 
reduce  materially  its  value  as  a  foundation.  In  some  parts  of 
Florida,  where  frost  is  not  to  be  feared,  if  the  sand  which  pre- 
vails is  held  in  place  by  curbs  or  planks  and  thoroughly  rolled 
while  damp,  it  makes  a  hard,  unyielding  support  not  subject  to 
disturbance  if  good  drainage  is  assured.  On  the  other  hand,  the 
black  soil  of  the  prairie  States,  which  absorbs  water  freely  and 

1  Mr.  Marr  states:  "Experience  in  Illinois  demonstrates  beyond  ques- 
tion that  curbs  are  not  needed  under  such  conditions.  We  have  had  sev- 
eral instances  where  the  edges  of  the  bricks  were  exposed  at  intersections 
to  a  grinding  action  of  wheels  striking  them  at  acute  angles,  and  there 
seems  to  be  absolutely  no  danger  of  the  bricks  being  loosened  at  the  edges 
under  any  conditions  obtaining  in  ordinary  service. 


164  AMERICAN   HIGHWAY   ASSOCIATION 

parts  with  it  slowly,  is  an  unstable  material  and  a  strong  con- 
crete foundation  must  be  provided  for  brick  roads  built  over  it, 
so  that  any  differences  in  the  supporting  capacity  of  the  subgrade, 
from  one  season  to  another  or  between  adjoining  places  in  the 
road,  are  equalized  by  the  concrete  slab  and  do  not  cause  waves 
in  the  brick  surface. 

The  methods  of  constructing  the  road  bed  and  preparing  the 
subgrade  are  explained  in  the  chapter  on  earth  roads.  It  is 
necessary  to  have  a  uniformly  firm  subgrade,  and  if  there  are 
heavy  cuts  and  fills  the  grading  must  be  done  carefully.  It  is 
desirable  to  allow  the  subgrade  to  go  through  one  winter  before 
putting  down  the  pavement,  although  this  is  rarely  practicable 
under  the  usual  working  conditions.  The  drainage  is  particularly 
important,  on  account  of  the  difficulty  of  improving  it,  if  defec- 
tive, after  the  pavement  is  laid. 

If  the  subgrade  is  firm  and  well  drained,  a  6  to  8-inch  base  of 
good  gravel,  broken  stone,  vitrified  clay1  or  slag,  thoroughly 
consolidated  by  rolling,  may  prove  sufficient  for  moderate  traffic. 
Such  a  base  should  be  built  in  two  courses  with  all  the  care  given 
to  the  best  macadam  construction.  In  some  cases,  second  qual- 
ity paving  bricks  have  been  used  for  a  base.  The  subgrade  is 
covered  with  enough  sand  to  give  a  depth  of  2  inches  after  roll- 
ing with  a  hand  roller.  The  No.  2  bricks  are  laid  flat  on  this 
cushion,  parallel  with  the  curb,  and  the  joints  are  filled  with  fine 
sand. 

The  best  base  for  general  use  is  concrete.  A  few  years  ago 
there  was  a  general  opinion  that  it  should  be  6  inches  thick,  but 
4-inch  bases  on  well-built  subgrades  are  giving  satisfaction  where 
frost  action  is  not  serious,  and  a  thickness  of  only  3  inches  or  less 
is  under  consideration  by  some  engineers.  If  a  secure  subgrade 
is  provided,  the  best  thickness  is  in  part  determined  by  the  cost 
of  the  concrete.  A  1 : 3 J  :  6  mixture  with  ordinary  materials, 
laid  to  form  a  5-inch  base,  may  be  less  expensive  than  a  1 :  2| :  5 
mixture  of  better  materials  laid  to  form  a  4-inch  base.  If  gravel 
is  used  as  the  aggregate,  it  is  generally  economical  to  screen  it  and 
then  recombine  it,  if  good  concrete  is  desired.  If  good  concrete 
is  not  desired,  it  will  be  better  to  leave  out  the  cement  entirely 
and  use  the  money  thus  saved  in  putting  down  a  good  base  of  the 

1  Mr.  Hinkle  advises  eliminating  gravel  and  vitrified  clay  as  materials 
for  a  base  for  this  reason:  "While  fair  foundations  may  be  made  from 
these  materials,  it  so  frequently  happens  that  poor  foundations  result 
from  the  use  of  these  materials  that  I  think  it  well  to  omit  referring  to 
them  here  and  hence  not  encourage  their  use  any  more  than  necessary." 
Mr.  Blair  believes  that  the  long  experience  with  gravel  foundations  in 
places  like  South  Bend,  Ind.,  warrants  their  use. 


BBICK  ROADS  165 

macadam  type.1  The  thinner  the  base,  the  better  the  concrete 
should  be.  A  4-inch  base  of  poorly  graded,  dirty  aggregate  and 
a  pinch  of  cement  is  an  invitation  to  early  failure.  One  common 
defect  is  insufficient  mixing.  This  should  be  done  hi  a  batch 
mixer  which  should  be  run  between  15  and  20  revolutions  per 
minute,  and  after  all  the  materials  are  in  the  mixer,  the  process 
should  be  continued  until  the  mixer  has  made  at  least  15  revo- 
lutions. The  surface  of  the  concrete  should  be  struck  off  by 
means  of  a  transverse  templet,  drawn  along  the  side  forms,  and 
be  kept  well  wet  for  at  least  three2  days.  No  traffic  should  be 
permitted  on  the  base  for  at  least  seven  days  after  it  is  laid.  On 
the  Illinois  state  highways,  if  there  are  deviations  exceeding  J 
inch  from  the  desired  shape  of  the  surface,  they  must  be  repaired 
if  a  sand-cement  cushion,  described  later,  is  to  be  employed. 

The  Cushion  or  Bedding  of  the  Bricks 

One  of  the  causes  which  contributed  to  limit  the  serviceability 
of  some  early  brick  pavements  was  the  imperfect  way  in  which 
the  bricks  were  supported  on  the  base.  The  latter  was  covered 
with  loose  sand  of  inferior  quality  for  its  purpose,  smoothed  off 
roughly  without  being  consolidated,  and  the  bricks  laid  on  it  and 
driven  to  a  bearing  with  a  paver 's  tamper.  The  joints  were 
then  filled  with  sand  and  the  roadway  thrown  open  to  travel. 
The  surface  was  not  smooth  at  the  outset,  traffic  on  it  soon  forced 
some  bricks  down  more  than  others,  and  water  percolating  in 
cold  weather  through  the  joints  into  the  sand  cushion  alternately 
froze  and  thawed,  throwing  the  bricks  into  irregular  positions. 
Under  such  conditions  the  edges  of  the  bricks  became  chipped, 
and  finally  many  of  the  bricks  became  broken  and  dislodged, 
leaving  holes  in  the  roadway.  The  lesson  of  this  experience  was 
so  clear  that  for  a  number  of  years  the  importance  of  bedding 
the  brick  securely  has  been  generally  recognized.  Today  there 
are  three  methods  of  doing  this,  termed  the  sand  cushion,  sand- 
cement  or  dry  mortar  bed  and  monolithic  or  green  concrete  bed 
types.  The  purpose  of  each  is  to  support  the  bricks  securely  at 
the  proper  elevation  to  give  the  pavement  a  smooth  surface. 

Sand-Cushion  Type. — A  sand  cushion  is  primarily  intended  to 
smooth  out  the  inequalities  in  the  top  of  the  base,  which  were 
formerly  greater  than  good  practice  now  permits,  to  provide  for 
the  slight  variations  in  the  depth  of  the  bricks.  Experience 

1  Mr.  Tebbs  advises  the  use  of  concrete  exclusively  as  a  base  for  brick 
pavements.  Mr.  Blair  holds  that  experience  at  Cleveland,  Terre  Haute 
and  other  places  shows  that  under  proper  conditions  a  base  of  other  ma- 
terial will  prove  satisfactory. 

1  Mr.  Hinkle  advocates  at  least  five  days. 


166  AMERICAN  HIGHWAY  ASSOCIATION 

shows  that  the  sand  must  be  free  from  large  stones,  which  pre- 
vent satisfactory  consolidation  of  the  cushion,  and  some  engi- 
neers hold  that  it  must  also  be  free  from  loam,  clay  and  materials 
of  a  greasy  nature  when  wet.1  Granulated  slag  is  sometimes 
used  instead  of  natural  sand  and  is  believed  by  some  engineers  to 
be  superior  to  ordinary  sand.  Dry  sand  must  be  used,  accord- 
ing to  some  engineers,  on  the  ground  that  wet  sand  shrinks  in 
drying  and  cannot  be  relied  upon  to  support  the  bricks  at  the 
desired  elevation.  Other  engineers  believe  that  somewhat  damp 
sand  is  more  easily  handled  and  gives  as  good  results.  The 
thickness  of  this  bed  in  the  case  of  city  streets  has  usually  been 
2  inches  of  late,  but  where  a  concrete  base  is  used  for  a  country 
highway  and  is  finished  so  that  no  part  deviates  more  than  J 
inch  from  the.  true  surface,  a  thickness  of  1J  inches  is  enough. 
On  narrow  roads  where  the  concrete  base  is  easily  finished  to  the 
exact  cross-section  of  the  road,  1  inch  is  probably  enough.2 

The  dry  sand  is  cast  over  the  base  to  a  slightly  greater  depth 
than  the  proposed  thickness  of  the  cushion.  The  extra  depth  is 
usually  about  \  inch  where  a  2-inch  cushion  is  desired.  A  plank 
templet,  which  is  often  provided  with  a  steel  edge,  is  then  drawn 
over  it  to  smooth  it  down  to  the  prescribed  cross-section.  If  the 
roadway  is  less  than  about  25  feet  wide,  this  templet  is  supported 
at  the  ends  by  the  curbs.  If  the  roadway  is  wider  than  25  feet, 
the  templet  is  long  enough  to  reach  from  one  curb  to  a  longitu- 
dinal plank  support  at  the  center  of  the  road.  The  sand  is  con- 
solidated and  brought  down  to  grade  by  rolling  it  by  hand,  using 
a  roller  weighing  300  to  400  pounds.  After  rolling  the  surface 
is  tested  with  the  templet,  the  high  spots  reduced  and  the  low 
places  filled,  and  the  rolling  repeated.  This  process  is  repeated 
until  a  uniform  surface  at  the  desired  elevation  is  obtained.  The 
extra  elevation  of  the  templet  in  the  first  stage  of  the  work  is 

1Mr.  Tebbs  makes  the  following  comments:  "Pennsylvania  specifica- 
tions allow  15  per  cent  of  loam  and  I  advocate  the  use  of  a  sand  contain- 
ing loam,  because  it  helps  to  bind  it,  thereby  avoiding  the  shifting  about 
which  often  occurs  with  clean  dry  sand.  It  has  been  proved  that  dry  sand 
occupies  less  space  than  wet  sand.  Dry  sand  cannot  always  be  obtained 
without  considerable  expense,  and  1  therefore  think  it  advisable  to  use 
reasonably  dry  sand  without  requiring  that  it  be  dried,  and  as  thin  a 
cushion  as  it  is  practicable  to  use.  The  cushion  should  be  1  inch  or  less. 
This  decrease  in  the  depth  of  the  cushion  minimizes  the  shrinkage  due  to 
the  drying  of  sand  which  was  moist  when  placed." 

2  Mr.  Marr  states:  "It  has  been  well  demonstrated  that  the  thinner 
the  sand  cushion  between  the  rigid  base  and  the  brick  wearing  surface, 
the  better,  and  its  only  function  is  to  assure  a  smooth  surface  on  the  pave- 
ment. The  use  of  the  plain  sand  cushion  is  growing  less  every  year  and 
seems  to  have  its  greatest  advantage  in  street  paving  where  numerous 
subsequent  openings  may  be  expected  and  it  is  necessary  to  use  a  soft 
filler." 


BRICK   ROADS  167 

obtained  by  laying  strips  of  wood  of  the  requisite  thickness  on 
top  of  the  curbs  or  other  supports  of  the  templet. 

If  a  road  carries  only  light  vehicles,  a  well  consolidated  sand 
cushion  is  a  satisfactory  support  for  the  bricks.  Heavy  vehicles, 
whether  drawn  by  horses  or  self-propelled,  are  believed  to  jar  the 
road  although  definite  tests  with  a  seismograph  or  a  similar  in- 
strument are  needed  to  determine  the  correctness  of  this  opinion. 
It  is  certain,  however,  that  if  the  roadway  contains  a  railway 
track  the  whole  structure  will  be  jarred  by  the  cars  traveling  along 
it.  The  sand  cushion  is  not  considered  by  many  engineers  to 
be  a  satisfactory  support  for  bricks  likely  to  be  jarred,  on  account 
of  the  possibility  that  the  repeated  minute  vibrations  in  it  may 
cause  parts  of  it  to  shift  their  position.  This  apprehension  has 
led  to  the  use  of  the  sand-cement  bed. 

Sand-cement  Cushion  Type. — The  cushion  consists  of  a  dry 
mixture  of  one  part  of  cement  with  three  to  five  parts  of  mortar 
sand.  These  materials  must  be  thoroughly  mixed  dry.  If  the 
cushion  is  to  be  1  inch  thick,  as  in  Pennsylvania  state  work,  the 
mixture  contains  less  cement  than  if  it  is  to  be  f  inch  thick  as 
in  the  Illinois  State  work.  The  loose  material  is  given  about  } 
inch  greater  depth  than  the  desired  thickness  of  the  finished  bed. 
The  mortar  is  spread  and  shaped  like  a  sand  cushion.  In  Illi- 
nois, where  the  sand-cement  bed  has  been  used  extensively,  the 
shaping  of  the  bed  for  the  brick  is  considered  of  prime  importance 
and  the  State  highway  department  requires  the  contractor  to 
employ  skilled  men  for  this  part  of  the  work. 

There  is  a  difference  of  opinion  as  to  the  best  method  of  moist- 
ening the  sand-cement  bed  to  convert  it  into  mortar.  Some 
engineers  hold  that  the  bricks  should  be  laid  on  the  dry  bed  and 
rolled,  and  then  the  pavement  should  be  sprinkled  sufficiently 
to  allow  water  to  pass  down  the  joints  into  the  bed.  This 
wetting  down  should  be  done  as  soon  as  the  bricks  have  been 
rolled.  The  Pennsylvania  highway  department  requires  the 
mortar  bed  to  be  sprinkled  lightly  just  before  the  bricks  are  laid. 
In  any  case,  the  mortar  bed  should  not  be  laid  so  far  in  advance 
that  any  of  it  will  remain  exposed  over  night,  and  if  any  of  it  be- 
comes wet  and  the  cement  sets  it  must  be  replaced  by  dry  material. 

Monolithic  Type.1 — The  monolithic  or  green  concrete  bed  is  not 
actually  a  cushion,  for  the  bricks  are  laid  on  the  fresh  concrete 
base  as  soon  as  it  has  been  finished.  In  this  type  of  work  steel 
side  forms  for  the  base  are  generally  specified  and  curbs  are 

1 A  monolithic  brick  pavement  was  laid  about  1904  in  Terre  Haute,  Ind., 
on  the  recommendation  of  Street  Commissioner  Varrelman  of  St.  Louis. 
It  was  on  a  railroad  teaming  yard  and  a  private  street  to  the  warehouse  of 
Hullmann  &  Company.  This  is  probably  one  of  the  earliest  uses  of  the 
type  in  this  country. 


168  AMERICAN   HIGHWAY   ASSOCIATION 

omitted.    The  steel  forms  are  considered  necessary  as  supports  for 
the  heavy  steel  templet  which  is  used. 

The  concrete  is  placed  in  successive  batches  for  the  entire 
width  of  the  pavement  in  a  continuous  operation.  This  concrete 
as  placed  has  a  slightly  greater  depth  than  the  finished  thickness 
of  the  base,  and  the  workmen  are  guided  in  placing  it  by  a  light 
wood  templet  which  rests  on  the  side  forms  when  in  use.  When 
it  has  been  brought  to  a  smooth  surface  of  the  desired  shape,  it 
is  finished  with  a  steel  templet.  This  consists  of  a  6-inch  steel 
I-beam  in  front  and  a  6-inch  steel  channel  at  the  rear,  held  2 
feet  apart  by  a  metal  frame  at  each  end.  Each  frame  has  two 
rollers  3  feet  or  more  apart.  These  rollers  rest  on  the  side  forms 
and  permit  the  templet  to  be  moved  ahead  easily  and  without 
jerks.  Both  beams  are  bent  to  the  desired  crown  of  the  pave- 
ment. The  lower  flange  of  the  I-beam  is  f  to  -^  inch  lower  than 
that  of  the  channel.  The  space  between  the  two  beams  is  kept 
filled  with  dry  1 :  3  mortar,  thoroughly  mixed.  As  the  templet  is 
moved  along,  the  I-beam  shapes  the  fresh  concrete  accurately, 
and  the  channel  leaves  a  thin,  compacted  bed  of  mortar  on  its 
surface,  so  that  the  bricks  have  a  support  which  is  true  to  grade 
in  every  respect.  Experience  shows  that  particular  care  must  be 
taken  in  this  type  of  construction  to  use  concrete  which  will  not 
flow  but  will  quake.  If  it  flows  it  will  not  support  the  bricks 
and  if  it  does  not  quake  it  will  be  deficient  in  strength.  The 
bricklaying  should  follow  closely  behind  the  templet  before  the 
concrete  takes  its  initial  set,  and  the  workmen  are  required  to 
move  with  special  care  over  the  bricks  just  laid.  Some  engineers 
require  boards  to  be  laid  for  the  workmen  to  walk  and  stand  on. 

Delivering  and  Laying  Bricks 

In  case  the  bricks  are  not  tested  at  the  plant,  each  carload 
must  be  sampled  as  it  is  delivered  and  the  lot  should  not  be 
allowed  on  the  road  until  the  samples  have  been  tested  and  ap- 
proved. If  this  is  not  done,  imperfect  bricks  are  likely  to  find 
their  way  into  the  road,  and  the  work  of  roadside  inspection  is 
made  needlessly  expensive  and  prolonged.1 

1  Mr.  Hinkle  calls  attention  to  the  following  paragraphs  in  the  speci- 
fications of  the  Ohio  State  highway  department:  "If  all  the  bricks  in  a 
shipment  or  in  several  shipments  of  the  same  make  and  kind  of  bricks 
appear  to  be  uniform  in  quality  two  samples  of  12  each  may  suffice^  If 
in  a  shipment  there  appears  to  be  different  classes  of  bricks,  such  as  bricks 
that  appear  to  be  more  or  less  burned  than  others,  a  representative  lot 
of  12  bricks  is  to  be  secured  for  each  class  of  bricks,  exclusive  of  the  culls. 
The  approximate  number  of  each  class  sampled  should  be  given  on  the 
notification  card  accompanying  the  samples.  Unless  otherwise  ordered 
by  the  Engineer,  at  least  one  lot  of  samples  should  be  taken  for  every 


BRICK   ROADS  169 

Bricks  are  liable  to  considerable  injury  if  handled  roughly, 
and  to  prevent  such  injury  to  them  after  their  acceptance  by 
test  many  engineers  specify  the  manner  in  which  they  shall  be 
handled.  The  requirements  of  the  Illinois  highway  department 
are  as  follows: 

Before  the  fine  grading  is  finished,  the  bricks  shall  be  hauled  and  neatly 
piled  without  the  edging  line  in  sufficient  quantities  to  complete  the  brick 
surface.  Clamps  and  conveyors  may  be  used  in  connection  with  the 
work  but  the  bricks  shall  not  be  dumped  from  industrial  cars  or  vehicles, 
nor  shall  they  be  thrown  to  piles  or  to  industrial  cars  or  to  vehicles.  The 
bricks  shall  not  be  piled  in  any  place  where  they  will  be  likely  to  be  be- 
aplattered  or  covered  with  mud  or  otherwise  injured.  In  delivering  the 
bricks  from  the  piles  for  placement  in  the  pavement,  no  wheeling  in  bar- 
rows will  be  allowed  ofc  the  brick  surface,  but  they  shall  be  carried  on 
pallets.  They  shall  be  placed  upon  the  pallets  so  that  when  delivered  to 
the  dropper  they  will  lie  in  such  order  that  each  brick  in  the  regular  oper- 
ation of  placing  it  upon  the  foundation  as  prepared,  will  bring  the  lugs  in 
the  same  direction  with  the  best  side  uppermost. 

The  bricks  are  laid  with  the  best  side  up  and  the  projections 
for  spacing  all  in  the  same  direction;  in  highway  work  they  are 
laid  in  rows  or  courses  at  right  angles  to  the  curb.  Alternate 
rows  commence  with  a  half  brick  at  the  curb  and  the  joints  in  a 
row  must  be  at  least  3  inches  from  those  in  the  row  last  laid. 
When  the  row  reaches  the  curb  towards  which  it  is  laid  it  must  be 
completed  with  a  bat  at  least  3  inches  long.  The  fractured  end 
of  a  broken  brick  must  be  toward  the  center  of  the  road.  Brick 
layers  generally  carry  three  or  four  rows  across  the  roadway 
simultaneously,  as  this  enables  them  to  save  considerable  walk- 
ing. The  bricks  are  laid  from  the  bricks  already  in  place,  and 
no  walking  is  permitted  on  the  cushion  or  dry  mortar  bed.  In 
order  to  keep  the  cross  joints  of  uniform  width,  after  about  six 
or  eight  rows  have  been  laid,  a  4  x  4-inch  timber  3  feet  long  is 
moved  along  the  face  of  the  last  row  and  tapped  lightly  with  a 
sledge. 

After  the  bricks  are  laid  the  surface  is  swept  clean  and  inspected. 
The  soft  bricks  are  replaced  by  good  ones;  they  are  detected  by 

100,000  bricks,  care  being  taken  to  secure  bricks  from  different  parts  oJ 
the  cars  or  piles  so  that  the  samples  submitted  will  be  representative  of 
the  bricks  to  be  used.  If  at  any  time  a  shipment  of  bricks  is  received  in 
which  the  quality  of  the  bricks  does  not  appear  equal  to  that  of  the  sam- 
ples previously  submitted,  additional  samples  should  be  immediately 
sent  to  the  testing  laboratory.  A  sufficient  number  of  samples  in  every 
case  should  be  taken  to  insure  the  use  of  bricks  of  proper  quality,  but  it 
should  be  borne  in  mind  that  the  charges  for  transportation  are  high  and 
only  a  sufficient  number  of  samples  should  be  submitted  for  test,  which 
will  permit  of  proper  control  of  the  quality  of  bricks  used." 


170 


AMEKICAN   HIGHWAY  ASSOCIATION 


Thousands  of  Bricks  Required  to  Pave  a  Mile  of  Road  of  Different 
Widths  with  Different  Numbers  of  Bricks  per  Square  Yard 


BRICK  PER 
SQUARE 
YARD 

WIDTH  OF  STREET 

8 

10 

12 

15 

18 

20 

22 

33 

174.2 

193.6 

232.3 

290.4 

348.5 

387.2 

425.9 

34 

179.5 

199.5 

239.4 

299.2 

359.0 

398.9 

438.8 

35 

184.8 

205.3 

246.4 

308.0 

369.6 

410.7 

451.7 

36 

190.0 

211.2 

253.4 

316.8 

380.1 

422.4 

464.7 

37 

195.3 

217.1 

260.5 

325.6 

390.7 

434.2 

476.9 

38 

200.6 

222.9 

267.5 

334.4 

401.3 

445.9 

490.5 

39 

205.9 

228.8 

274.6 

343.2 

411.7 

457.6 

503.4 

40 

211.2 

234.7 

281.6 

352.0 

422  .4 

469.4 

516.3 

41 

216.5 

240.5 

288.6 

360.8 

432.9 

481.1 

529.2 

42 

221.8 

246.4 

295.7 

369.6 

443.5 

492.8 

542.1 

43 

227.1 

252.3 

302.7 

378.4 

454.1 

504.6 

555.0 

44 

232.3 

258.1 

309.8 

387.2 

464.6 

516.3 

567.9 

45 

237.6 

264.0 

316.8 

396.0 

475.2 

528.0 

580.8 

46 

242.9 

269.9 

323.8 

404.8 

485.8 

539.8 

593.7 

dampening  the  surface  of  the  road  for  they  absorb  moisture 
more  quickly  than  the  others.  Bricks  which  are  badly  broken, 
spawled  or  misshaped  are  turned  over  or  replaced  by  good  ones, 
but  slight  chipping  of  the  corners  is  not  considered  serious.1 
The  surface  is  then  rolled,  for  which  purpose  a  tandem  self-pro- 
pelled roller  weighing  2\  to  4  tons  is  employed  where  a  sand 
cushion  is  used  and  a  hand  roller  about  2|  feet  long  and  2J  feet 
in  diameter,  weighing  about  600  pounds,  is  preferred  for  mono- 
lithic pavements.  The  rolling  should  begin  at  one  side  of  the 
road  and  proceed  back  and  forth  on  lines  slightly  inclined  toward 
the  center  of  the  roadway.  When  the  center  is  reached  the  roller 
should  be  used  on  the  other  side  of  the  road  in  the  same  way. 
Parts  of  the  pavement  which  cannot  be  reached  by  the  roller 
are  rammed  with  a  paver's  tamper  weighing  about  50  pounds, 
the  blows  being  struck  on  a  2-inch  plank  10  to  12  inches  wide 
and  at  least  6  feet  long. 

After  the  rolling,  the  pavement  is  again  inspected  and  any 
bricks  which  have  been  broken  or  seriously  injured  are  replaced. 
The  joints  are  examined,  and  if  the  sand-cushion  has  been  forced 
up  into  them  more  than  \  inch  in  the  sand-cushion  type,  the 
bricks  are  lifted  out,  the  cushion  reshaped,  and  the  bricks  relaid. 
This  inspection  of  the  joints  is  only  necessary  where  a  sand  cushion 
is  used. 

1  Mr.  Hinkle  considers  that  it  is  very  desirable  for  all  defective  bricks 
to  be  culled  out  before  the  bricks  are  laid  in  the  pavement.  This  will  not 
only  save  the  expense  of  replacing  the  defective  bricks  with  good  ones, 
but  will  avoid  disturbing  the  cushion.  This  is  more  important  with  the 
monolithic  than  with  other  types  of  pavement. 


BRICK  ROADS 


171 


Filling  Joints 

Joints  between  the  bricks  are  filled  with  sand,  cement  grout 
or  bituminous  material.  Sand  is  objectionable  because  it  gives 
very  little  support  to  the  bricks,  allows  their  edges  to  become 
chipped,  and  permits  water  to  percolate  down  into  the  cushion. 
It  is  no  longer  employed  except  for  roads  for  light  travel,  where 
the  saving  in  first  cost  is  considered  more  important  than  the 
probability  that  maintenance  expenses  will  become  high  at  an 
early  date. 

Grout  Fillers. — The  grout  filler  is  strongly  advocated  by  many 
engineers  on  the  ground  that  it  holds  the  bricks  firmly  and  does 


I 

-{ 


Height,  Z$* 


neignt,  25" 

VtfiHi  of  Box,      f  { Depth  of 


Height ,29" 
OepffjofBox, 

I     ii*  r  \*u  i  9  f,^ 

A  Depth  of 
'  \Box.l2'' 


Box  FOR  MIXING  GROUT 


not  wear  away  more  rapidly  than  the  vitrified  clay.  This  claim 
rests  upon  the  assumption  that  good  grouting  is  done,  for  poor 
joints  of  this  type  are  chipped  out  by  horses'  shoes  and  thus  al- 
low the  edges  of  the  bricks  to  become  broken.  If  the  grouting 
is  properly  done  this  will  not  happen.1  It  is  extremely  im- 

1Mr.  Marr  states:  "The  cement-grouted  pavement  seems  to  be  tbe 
most  satisfactory  for  country  highways,  and  this  has  led  us  in  our  studies 
in  Illinois  to  attach  great  importance  to  the  perfection  of  the  grout  filler. 
We  have  been  working  along  the  line  that,  theoretically,  the  earth  itself 
is  the  foundation  for  the  pavement  and  is  in  itself  wholly  adequate,  if  it 
is  thoroughly  settled  and  properly  drained.  In  other  words,  we  hold  that 
ordinary  dry  earth  sustains  any  load  which  we  place  upon  it  while  it  is 


172  AMERICAN  HIGHWAY  ASSOCIATION 

portant,  however,  with  cement  filler  that  a  rigid  foundation  be 
secured. 

Grout  for  filling  joints  should  be  made  of  equal  parts  of  cement 
and  clean,  sharp,  sand  mixed  thoroughly  while  dry.  As  a  gen- 
eral rule,  all  of  it  should  pass  a  No.  10  sieve  but  not  more  than  30 
per  cent  should  pass  a  screen  having  50  meshes  to  the  inch. 
After  the  sand  and  cement  are  thoroughly  mixed  dry,  water  is 
added  to  bring  the  mass  to  a  conolition  somewhat  thinner  than 
thin  cream,  so  it  will  flow  into  the  joints  without  any  separation 
of  its  ingredients.  The  mixing  is  kept  up  continuously,  either 
in  a  small  batch  mixer  or  the  box  shown  in  the  accompanying 
illustration.  The  tendency  on  extensive  work  is  to  use  a  batch 
mixer  equipped  so  it  can  be  used  for  applying  the  grout.  If  the 
box  is  used,  about  2  cubic  feet  of  the  dry  mixture  is  made  into 
mortar  in  each  batch.  The  best  grout  is  obtained  when  the 
water  is  added  slowly. 

The  surface  of  the  pavement  to  be  grouted  is  cleaned,  well 
wet,  and  then  covered  with  enough  grout  to  about  fill  the 
joints.  The  grout  is  taken  from  the  mixing  box  in  scoops  and 
after  it  is  poured  from  them  it  is  swept  into  the  joints,  usually 
with  coarse  rattan  brooms.  After  a  50-foot  section  of  road  has 
had  the  joints  filled  in  this  manner,  and  before  the  grout  first 
poured  begins  to  set,  a  somewhat  thicker  grout  is  made  and 
applied  on  the  same  surface.  It  is  brushed  into  the  joints  with 
squeegees  having  rubber  edges  where  they  rest  on  the  pavement. 
This  process  of  applying  the  relatively  thick  grout  and  brushing 
it  into  the  joints  with  squeegees  is  continued  until  the  joints  are 
completely  filled.  It  is  very  desirable  to  apply  the  grout,  so  far 
as  possible,  to  the  exact  parts  of  the  pavement  where  it  is  to  fill 
the  joints.  If  any  great  excess  of  grout  is  applied  at  one  place  in 
the  pavement  and  swept  to  another  place,  the  cement  and  sand 
are  liable  to  become  separated  and  defective  grout  will  result. 
If  the  bricks  have  rounded  edges,  the  squeegees  should  be  pressed 

in  this  condition,  and  that  the  real  problem  is  to  keep  it  in  this  condition 
by  covering  and  waterproofing  it  with  some  material  which  will  withstand 
the  abrasive  action  of  traffic.  This,  in  turn,  leads  us  to  believe  that  if  we 
use  a  thin  base,  such,  for  instance,  as  2  inches  of  sand  and  cement  mixed, 
or  even  1  inch,  or  even,  theoretically,  i  inch,  the  properly  grouted  bricks 
will  then  withstand  successfully  the  action  of  any  such  traffic  as  we  have 
at  the  present  time. 

"The  mortar  bed  has  for  its  prime  function  the  insurance  of  a  perfect 
grout  joint,  by  preventing  earth  or  other  foreign  matter  from  working 
up  into  the  bottom  of  the  joints  during  construction.  It  has  a  secondary 
value  in  enabling  us  to  obtain  a  smoother  wearing  surface  by  facilitating 
the  proper  grading  of  the  bed  on  which  the  bricks  lie  by  the  use  of  mechan- 
ical methods  such  as  templets.  We  have  built  a  6-mile  stretch  of  brick 
road  9  feet  wide,  on  a  1-inch  mortar  bed  base,  which  1  believe  will  demon- 
strate the  correctness  of  the  theory  we  are  now  holding." 


BRICK  ROADS 


173 


firmly  against  them  on  the  last  brushing  so  that  no  thin  edges 
of  grout  will  remain  on  the  surface,  for  they  break  away  very 
soon  and  are  liable  to  pull  a  part  of  the  joint  filler  with  them. 

To  prevent  the  grout  from  flowing  through  the  joints  beyond 
the  limits  of  the  section  where  the  filling  is  being  done,  strips  of 
fa  inch  steel  6  inches  wide  and  3  feet  long  are  inserted  in  the 
last  transverse  joint,  to  act  as  a  dam  until  after  the  initial  set  of 
the  cement. 

After  the  surface  has  been  inspected,  it  is  the  practice  in  Illi- 
nois to  cover  it  with  sand,  which  is  kept  wet  for  ten  days,  and  no 
travel  is  permitted  on  the  road  for  three  weeks  after  the  grout 
has  been  poured.  In  Ohio  and  Pennsylvania,  the  sand  is  kept 
damp  for  at  least  five  and  four  days  respectively,  and  travel  is 
kept  off  for  at  least  ten  days.  In  New  York  travel  is  kept  off 
for  ten  days,  and  the  covering  must  be  kept  moist  for  that  period. 
The  National  Association  of  Paving  Brick  Manufacturers  ad- 
vises keeping  the  covering  wet  for  four  days  and  travel  off  the 
road  for  fifteen  days. 

Bituminous  Fillers. — Bituminous  fillers  vary  greatly  in  qual- 
ity, and  the  experience  with  some  of  the  materials  tried  has  not 
been  satisfactory.  The  filler  should  not  become  soft  during  hot 
weather  nor  brittle  during  cold  weather,  it  should  adhere  to  the 
bricks,  and  it  should  not  be  injured  by  water.  A  1 : 1  bituminous- 
sand  mastic  filler  has  recently  been  used  considerably.  Ob- 
viously climatic  conditions  should  govern  the  selection  of  the 
material  in  some  degree,  for  a  filler  suitable  for  the  brick  pave- 
ments of  Florida  might  prove  unsatisfactory  during  a  New 
England  winter. 

The  Ohio  State  requirements  for  asphalt  fillers  are  as  follows : . 

Specific  gravity,  0.98  to  1.04. 

Solubility  in  chemically  pure  carbon  disulphide,  at  least  99^ 
per  cent. 

Matter  soluble  in  86°B.  paraffin  naphtha,  25  to  40  per  cent. 

Limits  for  penetration 


TEMPERATURE 

NEEDLE 

WEIGHT 

TIME 

PENETRATION 

°C. 

grams 

25 

No.  2 

100 

5  sec. 

2.5  to  5  mm. 

4 

No.  2 

200 

1  min. 

2  mm.  or  more 

46 

No.  2 

50 

5  sec. 

10  mm.  or  less 

Melting  point  by  cube  method,  80°C.  to  120°C. 
It  shall  be  free  from  water  and  not  foam  when  heated  to  350°F. 
The  Ohio  State  requirements  for  coal  tar  pitch  fillers  are  as 
follows : 


174  AMERICAN  HIGHWAY   ASSOCIATION 

Specific  gravity  at  25°C.,  1.23  to  1.3. 

lYee  carbon  on  extraction  with  carbon  disulphide,  20  to  40 
per  cent. 

Inorganic  matter  on  ignition,  0.5  per  cent. 

Melting  point  by  cube  method,  57°C.  to  63°C. 

It  shall  be  free  from  water  and  not  foam  when  heated  to  300°F. 

These  bituminous  fillers  are  used  hot  and  the  bricks  should 
therefore  be  dry  when  the  joints  are  poured.  If  a  sand-cement 
bed  is  used,  the  water  for  it  must  be  applied  through  the  joints, 
if  it  is  added  in  that  way,  long  enough  before  the  joints  are  filled 
to  permit  them  to  become  dried  out. 

The  filler  is  melted  in  a  kettle,  from  which  it  is  usually  drawn 
into  funnel-shaped  pourers  terminating  in  a  nozzle  having  an 
opening  about  J  inch  in  diameter,  with  a  valve  by  which  the 
flow  through  it  can  be  regulated.  This  is  held  over  the  joint, 
with  the  nozzle  projecting  into  it,  and  carried  along  slowly.  The 
joints  are  somewhat  overfilled  by  the  pourer,  on  the  theory  that 
the  early  travel  on  the  pavement  will  force  some  of  the  surplus 
material  into  the  joint  and  make  it  more  dense.  After  the  joint 
is  poured,  some  engineers  have  it  dusted  over  with  sand,  and  it 
is  customary  to  keep  traffic  off  the  pavement  until  the  filler  has 
cooled. 

A  mixture  of  tar  and  sand,  called  a  " mastic  filler,"  has  been 
used  to  some  extent.  The  hot  tar  and  heated  sand  are  mixed 
in  equal  volumes.  A  softer  grade  of  tar  is  used  in  the  mixture 
than  that  called  for  by  the  Ohio  specification  for  a  tar  filler. 
This  mastic  filler  is  flushed  into  the  joints  by  pouring  it  onto  the 
pavement  and  spreading  it  with  a  squeegee. 

It  is  particularly  desirable  to  roll  the  bricks  and  fill  the  joints  to 
within  at  least  50  feet  of  the  bricklaying  work.  If  rain  falls  and 
the  cushion  becomes  saturated,  it  is  impossible  to  roll  the  bricks 
to  a  firm  condition,  for  the  wet  sand  allows  them  to  rock  and  the 
cushion  is  forced  up  into  the  joints.  By  lifting  out  a  brick  here 
and  there,  the  height  of  the  sand  in  the  joint  can  be  seen  and  the 
character  of  the  rolling  judged  from  it. 

Expansion  Joints 

In  the  early  days  of  brick  street  pavements,  the  bricks  at  the 
crown  of  a  street  occasionally  rose  in  summer  as  a  result  of  the 
expansion  of  the  pavement  by  heat.  To  remedy  this,  joints 
filled  with  some  compressible  material  were  laid  along  one  or 
both  curbs,  and  some  engineers  used  similar  transverse  expan- 
sion joints  at  intervals  of  50  to  75  feet.  The  longitudinal  joints 
have  proved  useful,  but  there  is  some  question  as  to  the  value  of 
the  transverse  joints  in  street  pavements.  The  objection  to 
transverse  joints  is  that  they  are  worn  away  rather  rapidly  and 


BRICK   ROADS  175 

this  causes  the  travel  to  chip  off  the  edges  of  the  bricks  separated 
by  them.  Whenever  this  chipping  occurs  to  any  extent,  the 
pavement  soon  develops  a  rut  or  hole.  Cracks  in  a  country 
road,  if  properly  filled  when  they  first  open  and  kept  filled  after- 
ward, do  not  injure  it  appreciably,  and  it  is  generally  consid- 
ered that  transverse  joints  in  a  brick  wearing  surface,  to  prevent 
transverse  cracks,  are  more  likely  to  cause  than  prevent  trouble. 

Expansion  joints  are  of  two  types,  poured  and  prepared.  The 
former  are  made  by  placing  a  board  filler  of  the  thickness  of  the 
joint  against  the  curb  and  laying  the  bricks  against  it.  The 
Maryland  rule  for  the  thickness  of  the  joints  is  as  follows:  On 
streets  30  feet  or  more  wide,  1J  inches  next  each  curb;  on  20  to 
30-foot  streets,  1  inch  next  each  curb;  on  12  to  20-foot  streets,  J  inch 
next  each  curb;  on  streets  under  12  feet,  f  inch  next  one  curb.  In 
Pennsylvania  a  J-inch  joint  at  each  curb  is  specified.  On  the 
Illinois  brick  roads  with  a  sand-cement  base  a  f-inch  joint  along 
one  curb  is  used.  The  plank  filler  usually  consists  of  two  thin 
6-inch  boards  of  a  wedge-shape  cross-section,  dressed  on  both 
sides.  One  of  them  is  laid  against  the  curb  with  the  thin  edge  on 
the  base,  and  the  other  is  placed  against  it  with  the  thick  edge 
downward.  The  combined  thickness  of  the  two  is  equal  to  the 
thickness  of  the  joint.  Handles  are  attached  to  their  upper 
edges,  so  they  can  be  lifted  out  when  the  grout  filler  which  has 
been  poured  has  set.  The  filler  for  poured  expansion  joints  should 
meet  the  requirements  for  the  filler  for  other  joints  of  this  type. 
With  the  monolithic  and  sand-cement  cushion  types  of  pavement, 
the  joints  should  be  filled  as  far  as  the  bricks  are  laid,  each  day. 

Prepared  fillers  are  now  extensively  used.  They  are  strips 
of  bituminous  material  or  some  kind  of  felt  or  fabric  impreg- 
nated with  bituminous  material.  They  are  placed  against  the 
curb  and  the  bricks  laid  against  them,  thus  doing  away  with  the 
board  fillers  required  with  poured  joints  and  making  it  unneces- 
sary to  provide  heating  kettles  on  pavements  with  grouted 
joints. 

Experience  on  the  Pennsylvania  State  highways  has  shown 
that  a  prepared  filler  extending  the  full  depth  of  the  brick  some- 
times permitted  water  to  penetrate  from  the  road  surface  into 
the  cushion,  where  it  froze  and  heaved  the  bricks.  It  is  there- 
fore considered  advisable  on  that  work  to  have  the  prepared 
filler  stop  from  f  to  1  inch  below  the  surface  of  the  road  and  to 
fill  the  top  of  the  joint  with  hot  bituminous  material. 

Where  a  cement-sand  bed  is  used,  a  |  inch  prepared  expansion 
joint  extending  through  the  entire  pavement  is  recommended 
by  some  engineers;  it  is  placed  in  two  strips,  the  first  or  bottom 
strip  being  placed  in  the  concrete  base,  and  the  second  strip  im- 
mediately above  it  when  the  bed  and  bricks  are  laid. 


176  AMERICAN  HIGHWAY  ASSOCIATION 

Small  Cubical  Bricks 

Shortly  after  small  stone  blocks  were  introduced  in  Europe  for 
constructing  pavements  having  the  trade  name  of  "Durax,"  the 
county  superintendent  of  Monroe  County,  N.  Y.,  J.  Y.  McClintock, 
employed  cubes  measuring  2  to  2 J  inches  on  a  side  for  resurfacing 
old  macadam  roads  to  resist  motor  traffic.  In  1916  he  stated  that 
vitrified  clay  cubes  had  given  better  results  than  those  of  other 
materials.  Those  laid  in  1916  were  2J  inches  in  each  dimension, 
weighed  about  1  pound  each,  and  were  laid  225  to  the  square 
yard.  The  only  specification  for  the  cubes  is  that  they  must  not 
absorb  more  than  3  per  cent,  of  their  weight  when  immersed  in 
water.  They  have  been  laid  on  a  gravel  base,  broken  slag,  broken 
stone  and  concrete,  and  the  joints  are  filled  with  any  local  fine 
material.  It  is  considered  advisable  to  make  the  base  several 
feet  wider  than  the  roadway,  so  that  the  gravel  or  broken  stone 
shoulders  adjacent  to  the  cubes  shall  be  supported  rigidly  and 
the  tendency  for  the  border  cubes  to  become  displaced  will  be 
minimized. 

Aspha-Bric 

During  1915  and  1916  attention  was  directed  to  the  possibilities 
of  asphalt  impregnated  brick.  The  idea  of  impregnating  brick  with 
bituminous  material  is  not  new.  In  1893  brick  boiled  in  coal  tar 
were  laid  in  Portland,  Ore.,  and  remained  in  service  17  years. 
About  1907  nose  brick  boiled  in  asphalt  were  laid  along  the  tracks 
of  the  Los  Angeles  Electric  Railway  Corporation  and  2500  simi- 
lar brick  were  laid  along  tracks  in  San  Francisco  about  1912. 
Brick  boiled  in  bituminous  material  have  also  been  laid  in  Nash- 
ville and  Chattanooga. 

The  method  of  treating  brick  which  came  into  prominence  in 
1915  is  designed  to  fill  completely  the  pores  in  the  brick.  As  the 
porosity  of  different  grades  and  makes  varies  considerably,  the 
quantity  of  impregnating  material  required  will  range  from  about 
6  to  15  per  cent  of  the  volume  of  the  brick.  As  a  result  of  the 
treatment  it  is  claimed  that  the  brick  become  impervious  to  mois- 
ture, the  bituminous  jointing  material  adheres  more  firmly  to  the 
treated  than  to  the  untreated  brick,  and  the  wearing  properties, 
as  indicated  by  the  standard  rattler  test,  are  greatly  improved. 
This  last  advantage  is  indicated  in  the  accompanying  tabulation 
of  tests  of  untreated  and  treated  "second"  brick  conducted  by 
Robert  W.  Hunt  &  Company.  Each  test  was  made  with  five 
untreated  and  five  treated  brick,  225  pounds  of  small  shot  and  75 
pounds  of  large  shot,  the  rattler  making  1800  revolutions  at  the 
rate  of  30  revolutions  per  minute.  The  increase  in  wear  due  to 


BRICK   ROADS 


177 


Results  of  tests  of  untreated  and  asphalt  impregnated  brick.    Each  sample 
consisted  of  five  untreated  and  five  treated  brick 


SAMPLE 

l 

2 

Weight  in  pounds: 
Before  treatment  — 
After  treatment.  .   . 

50.66 
56.75 
6.09 

27.02 
8.38 

53.34 

14.77 

1 
0 

48.81 
54.01 
5.20 

17.39 
8.96 

35.63 
16.59 

0 
0 

46.50 
48.97 
2.47 

28.81 
6.22 

61.96 
12.70 

3 
3 

53.35 
55.77 
2.42 

17.19 
10.07 

32.22 
18.06 

0 
1 

45.25 
47.49 
2.24 

13.93 
6.51 

30.79 
13.71 

0 
0 

48.65 
51.33 
2.68 

11.88 
6.83 

24.42 
13.31 

0 
0 

49.75 
54.60 
4.85 

19.57 
7.36 

39.34 
13.48 

0 
0 

47.95 
49.94 
1.99 

13.63 
6.46 

28.43 
12.94 

0 
0 

50.03 
54.53 
4.50 

11.78 
6.25 

23.55 
11.46 

0 
0 

Asphalt  used  

Loss  in  weight,  pounds  : 
Untreated 

Treated 

Loss    in   weight,    per 
cent: 
Untreated  

Treated 

Broken  brick: 
Untreated  .  . 

Treated.  .  .          . 

impregnation  will,  it  is  stated,  enable  manufacturers  to  stop  their 
burning  at  a  lower  temperature  than  is  now  customarjr,  thus 
materially  reducing  the  number  of  poor  brick  in  a  kiln,  and  to 
obtain  the  necessary  strength  by  impregnating  the  brick.  It  is 
also  claimed  that  grades  of  brick  unsuitable  for  pavements  may 
be  made  into  satisfactory  pavers  by  impregnation.  For  example, 
impregnating  clay  building  brick  with  11.3  per  cent  of  asphalt 
gave  a  product  showing  9.3  per  cent  loss  in  the  standard  rattler 
test,  although  untreated  brick  showed  100  per  cent  loss  after  500 
revolutions.  Shale  building  brick  which  showed  42.4  per  cent 
loss  in  the  rattler  test  before  they  were  treated,  lost  only  17  per 
cent  after  treatment.  Sand-lime  brick  which  showed  100  per 
cent  loss  after  400  revolutions  lost  only  23  per  cent  after  being 
impregnated  with  10  per  cent  of  asphalt.  Impregnating  clay 
and  shale  building  brick  with  8J  per  cent  of  asphalt  reduced  the 
loss  in  the  rattler  test  from  40.9  to  14.2  per  cent.  The  impregna- 
tion of  the  brick  also  reduces  their  absorption  of  water  to  practi- 
cally nothing. 

The  asphalt-impregnating  process  begins  when  the  brick  are 
removed  from  the  kilns  or  dryers.  They  are  loaded  on  small 
cars  which  are  run  into  a  cylinder.  There  they  are  heated  to 
about  300 °F.,  which  expands  them,  and  a  vacuum  is  produced 
in  the  cylinder  to  remove  all  moisture  from  the  brick  and  leave 
their  pores  open.  The  cylinder  is  then  filled  with  a  special  grade 
of  asphalt  at  a  temperature  of  350°F.  and  the  cylinder  put  under 
heavy  pressure  until  the  gauges  show  that  impregnation  is  com- 
plete. The  asphalt  is  drained  off  and  pressure  again  applied 
until  the  brick  have  cooled.  During  cooling  they  contract  some- 
what, causing  the  asphalt  to  become  sealed  in  the  pores. 


A  BRICK  PAVEMENT  ON  A  ONE-INCH   CON- 
CRETE BASE' 

A  brick  pavement  was  laid  in  1917  in  Stockland  township, 
Iroquois  County,  Illinois,  on  a  one-inch  concrete  base.  This 
pavement  is  9  feet  wide,  and  the  contract  is  for  about  6J  miles, 
of  which  about  3  miles  has  been  constructed.  The  contract 
price  for  this  work  is  approximately  $8700  a  mile,  of  which  about 
$300  is  for  bridges  and  culverts  and  about  $450  for  grading. 
The  price  for  the  slab  alone  is  $1.50  per  square  yard. 

This  pavement  is  being  laid  on  an  old  gravel  road  for  a  foun- 
dation and,  in  order  to  secure  the  full  benefit  of  this  old  material, 
the  gradient  of  the  new  pavement  varies  but  slightly  from  that 
of  the  present  road.  By  not  disturbing  the  old  gravel,  it  has 
been  possible  to  secure  a  very  firm  subgrade  and  we  have  no  doubt 
but  the  pavement  will  prove  very  satisfactory.  The  concrete 
base  is  composed  of  1  part  cement  to  2J  parts  fine  aggregate  and 
4  parts  coarse  aggregate.  The  fine  aggregate  consists  of  sand 
all  of  which  passes  a  J-inch  mesh.  The  coarse  aggregate  con- 
sists of  material  which  would  be  retained  on  a  t-inch  mesh  and 
passes  a  f-inch  mesh.  As  a  matter  of  fact,  there  is  very  little 
of  this  material  which  will  not  pass  a  f  inch  mesh  and  it  is  the 
same  type  of  gravel  that  is  commonly  used  for  roofing  purposes. 

I  have  no  doubt  but  this  pavement  would  be  practically  as 
good  as  if  the  brick  had  been  laid  directly  on  the  old  gravel  road, 
but  in  a  construction  of  this  kind,  it  is  necessary  to  have  some 
sort  of  a  concrete  base  in  order  to  secure  a  perfectly  smooth  and 
uniform  surface  on  which  to  lay  the  bricks. 

The  subgrade  was  thoroughly  rolled  and  all  soft  places,  of 
which  there  were  very  few,  were  removed  and  the  subgrade 
brought  up  to  a  true  plane  by  the  addition  of  fresh  material  which 
was  thoroughly  compacted.  Before  concrete  was  placed,  the 
subgrade  was  well  wet;  after  the  concrete  was  placed,  it  was 
struck  off  by  means  of  a  template  and  the  bricks  were  laid  di- 
rectly on  the  green  concrete. 

Two  brick  setters  were  used  on  this  job  and  by  having  a  brick 
hammer  on  each  side  of  the  road,  the  setters  not  only  started  but 
finished  the  courses,  as  on  a  pavement  of  this  width  no  bats,  except 

1  By  Rodney  L.  Bell,  Division  Engineer,  Illinois  State  Highway  De- 
partment. 

178 


BKICK   PAVEMENT  179 

one  half-sized  brick,  are  required  in  starting  and  finishing  the 
courses.  Bricks  were  carried  on  to  the  pavement  in  such  a  way 
that  the  good  side  of  the  bricks  was  always  placed  up  and  the 
lugs  all  in  one  direction.  By  requiring  the  brick  carriers  to  use 
some  care,  a  large  amount  of  the  culling  which  ordinarily  takes 
place  on  a  brick  road  was  eliminated.  Just  as  soon  as  the  bricks 
were  culled,  the  pavement  was  swept  and  the  rolling  started. 

One  man  did  nothing  but  keep  the  roller  moving  the  entire 
time.  It  was  a  small  hand  roller  about  30  inches  in  length  and 
24  inches  in  diameter  and  when  filled  with  water  weighed  about 
700  pounds.  This  weight  was  sufficient  to  secure  a  good  surface 
over  the  entire  length  of  the  pavement.  The  first  rolling  was 
begun  at  the  outer  edge  and  the  pavement  was  rolled  parallel  to 
the  center  line  of  the  pavement.  After  the  entire  surface  had 
been  covered  in  this  way,  the  pavement  was  cross-rolled  in  oppo- 
site directions,  the  roller  making  an  angle  of  about  45  degrees 
with  the  center  line  of  the  pavement. 

In  order  to  allow  plenty  of  time  to  secure  a  thorough  job  of 
rolling,  the  grouting  machine  was  kept  about  100  feet  behind  the 
brick  layer.  The  grout  mixture  consisted  of  one  part  cement  and 
1  part  of  sand  mixed  in  a  machine  designed  for  this  purpose.  It 
was  the  intention  to  practically  fill  the  joints  at  the  first  appli- 
cation so  that  after  the  grout  had  had  a  chance  to  settle,  it  would 
leave  from  J  to  f  inch  to  be  filled  with  subsequent  applications. 

The  second  application  of  the  grout  was  mixed  slightly  thicker 
than  the  first,  and  was  wheeled  back  over  the  pavement  from  the 
mixing  machine  rather  than  bother  with  moving  the  machine 
back  over  the  pavement  a  second  time.  This  application  was 
worked  into  the  joints  by  use  of  a  squeegee  and  on  the  final  going 
over,  the  squeegees  were  pulled  at  an  angle  of  about  45  degrees 
with  the  joints  in  order  to  secure  a  better  surface  and  to  keep 
the  grout  from  being  dragged  out  from  between  the  brick. 

After  the  grout  had  set  sufficiently,  the  pavement  was  covered 
with  1  inch  of  loose  dirt,  which  was  kept  wet  for  one  week.  The 
pavement  was  opened  to  traffic  after  it  had  been  down  three 
weeks. 

This  work  is  being  paid  for  by  a  bond  issue  which  has  been 
voted  by  Stockland  township,  Iroquois  County,  and  is  under 
the  general  supervision  of  Benj.  Jordan,  county  superintendent 
of  highways  of  Iroquois  County. 


HIGHWAY   BONDS1 

The  mathematical  theory  of  interest  as  applied  to  bond  cal- 
culations is  explained  in  a  section  of  Bulletin  136  of  the  United 
States  Department  of  Agriculture  which  has  tables  of  much 
value  to  those  making  a  detailed  examination  of  the  subject. 
For  the  usual  purposes  of  highway  officials,  however,  the  much 
simpler  tables  which  are  printed  herewith  are  not  only  sufficient 
in  scope  but  also  more  easily  used. 

The  bonds  used  almost  universally  until  a  few  years  ago  were 
of  the  sinking-fund  type.  Parties  issuing  them  have  to  provide 
annually  during  the  term  of  the  bonds  the  stipulated  interest 
and,  theoretically,  set  aside  a  sum  at  interest  which  will  amount 
at  the  end  of  the  term  to  the  principal  of  the  bonds.  This  an- 
nual sum  set  aside  at  interest  is  called  the  sinking  fund,  and  the 
amount  which  must  be  raised  for  such  a  fund  depends  upon  the 
interest  it  bears.  This  interest  is  usually  quite  low  in  comparison 
with  the  interest  paid  on  the  bonds. 

Unfortunately  the  financial  methods  of  public  officials  do  not 
always  remain  above  criticism  and  it  often  happens  that  the  annual 
payment  into  the  sinking  fund  is  forgotten  or  neglected.2  Some- 
times the  money  accumulated  in  the  sinking  fund  is  diverted 
from  its  purpose.  Such  departures  from  sound  finance  result  in 
a  lack  of  money  to  pay  off  the  bonds  when  they  become  due,  as 
agreed,  and  it  then  becomes  necessary  to  issue  a  new  series  of 
bonds  to  carry  this  indebtedness.  This  is  a  serious  matter  when 
the  improvements  for  which  the  bonds  were  issued  have  become  of  no 
further  use,  as  in  the  possible  case  of  a  worn-out  road  surface, 
or  obsolescent,  as  in  the  possible  case  of  an  overloaded  bridge, 
when  the  taxpayers  who  contribute  for  the  second  bond  issue  are 
obliged  to  pay  for  something  for  which  they  receive  little  or  no 
benefit.  This  is  not  equitable,  and  so  some  states  fix  the  term 
of  bonds  which  may  be  issued  to  pay  for  certain  classes  of  im- 

1  Revised  by  B.  K.  Coghlan,  associate  professor  of  highway  engineer- 
ing, Agricultural  and  Mechanical  College  of  Texas. 

'Baker,  Watts  &  Co.,  bankers,  of  Baltimore,  make  the  lollowing  com- 
ment: "We  view  it  as  a  very  serious  matter  to  neglect  the  sinking  fund, 
regardless  of  the  character  of  the  improvement  for  which  the  bonds  are 
issued.  We  think  that  public  officials  cannot  be  too  forcibly  impressed 
with  the  absolute  necessity  of  managing  public  funds  strictly  in  accordance 
with  the  laws  and  ordinances  authorizing  bond  issues,  and  any  neglect  or 
diversion  of  public  sinking  funds  should  be  summarily  dealt  with." 

180 


HIGHWAY   BONDS  181 

provements.  In  New  Jersey,  for  example,  the  term  of  bonds  for 
gravel  roads  is  limited  to  five  years,  waterbound  or  bituminous 
macadam  ten  years,  bituminous  concrete  fifteen  years,  6-inch 
concrete  twenty  years,  block  pavements  twenty  years,  sheet 
asphalt  on  a  concrete  base  twenty  years,  and  stone,  concrete 
and  iron  bridges  thirty  years.  The  useful  life  of  the  improve- 
ment is  what  must  be  considered,  and  this  is  determined  in  some 
cases  by  obsolescence  rather  than  depreciation,  notably  in  the 
case  of  bridges.  The  attractiveness  of  bonds  for  road  work 
would  be  enhanced  in  many  cases  if  an  equivalent  of  the  fol- 
lowing statute,  in  force  in  Mississippi,  were  generally  adopted: 

The  public  highway  or  highways  so  surveyed  and  adopted  by  such  com- 
missioners shall  be  constructed  and  maintained  out  of  the  proceeds  of 
such  bonds;  proceeds  of  such  bonds  to  be  used  alone  in  their  construction; 
and  the  board  of  supervisors  shall  levy  an  annual  tax,  on  the  recommen- 
dation of  such  commissioners,  on  all  the  taxable  property  in  such  district 
or  districts  of  not  exceeding  1  mill  on  the  dollar,  which  shall  be  used  to 
supplement  the  general  fund  of  the  county  in  maintaining  said  road  or 
roads  and  the  culverts,  bridges  and  levees  thereon. 

The  importance  of  maintenance  of  roads  is  so  great  that 
statutes  authorizing  bond  issues  for  construction  should  require, 
as  part  of  the  stipulations  under  which  the  bonds  are  issued,  an 
adequate  financial  provision  for  the  upkeep  of  the  roads  during 
the  term  of  the  bonds.  This  insures  a  full  statement  of  the 
financial  obligations  of  the  bond  issue  upon  the  taxpayers  before 
they  vote  on  the  issue. 

The  investment  of  the  sinking  fund  affords  an  indication  of 
the  financial  ability  of  a  community.  In  some  sections  of  the 
country,  the  investment  is  intrusted  to  special  boards  of  sinking 
fund  commissioners,  and  appointment  to  such  a  board  is  re- 
garded as  a  high  honor,  so  that  the  positions  are  filled  by  men  of 
the  highest  business  standing.  In  such  cases  the  community 
not  only  feels  confident  of  its  financial  stability  but  its  bond 
issues  are  sought  so  eagerly  that  it  is  not  necessary  to  pay  high 
rates  of  interest.  In  a  few  places,  sinking  funds  have  been 
neglected  and  the  financial  standing  of  the  community  suffers 
in  consequence. 

A  second  type  of  bond  is  known  as  the  annuity  bond.  An 
annuity  is  a  fixed  sum  paid  at  regular  intervals  of  time  for  either 
a  definite  term  or  for  the  life  of  the  beneficiary  of  the  annuity. 
An  annuity  bond  draws  interest  at  an  agreed  rate,  but  at  the 
close  of  each  retirement  period  stated  in  the  bond,  the  payment 
to  the  bondholders  includes  both  the  interest  that  has  accrued 
during  the  period  since  the  last  payment  and  enough  of  the 
principal  to  make  the  full  payment  a  definite,  uniform  amount 
at  the  close  of  each  retirement  period.  The  annual  payment  at 


182  AMERICAN   HIGHWAY  ASSOCIATION 

the  end  of  the  first  retirement  period  is  mainly  for  interest  and 
that  at  the  end  of  the  last  period  is  mainly  for  retiring  the  last 
of  the  outstanding  principal.  The  advantage  of  the  plan  is  that 
it  retires  some  principal  annually  and  thus  saves  the  taxpayer 
the  expense  of  paying  interest  on  the  whole  of  a  bond  issue  dur- 
ing its  term.  This  makes  annuity  bonds  less  expensive  than 
sinking  fund  bonds  to  the  county  issuing  them. 

The  annuity  bond  issue  possesses  the  advantage  of  requiring 
the  same  amount  to  be  raised  each  year,  during  its  term.  The 
annual  payments  must  be  adjusted,  however,  so  that  the  amount 
of  principal  retired  will  be  some  multiple  of  $100,  $500  or  $1000, 
or  whatever  sum  is  the  face  value  of  one  bond.  Consequently  the 
actual  payment  on  annuity  issues  at  the  end  of  a  retirement  period 
is  not  the  uniform  theoretical  amount  given  in  bond  tables  but 
an  amount  varying  slightly  from  it,  sometimes  more  and  some- 
times less.1 

The  serial  bond  issue  is  a  type  which  has  found  favor  with  both 
borrowers  and  lenders.  The  farmer  finds  it  desirable  because  it 
retires  each  year  a  part  of  the  principal,  and  is  thus  more  econom- 
ical than  a  sinking  fund  bond  issue.  The  purchasers  of  the  bonds 
like  them  because  there  is  a  strong  public  sentiment  in  favor  of 
serial  bonds,  which  gives  them  standing  as  a  good  type  of  invest- 
ment security.  It  is  the  least  expensive  method  of  borrowing 
money  by  issuing  bonds,  as  an  examination  of  the  accompanying 
tables  will  show. 

One  defect  of  serial  bonds  for  certain  classes  of  public  im- 
provements is  that  the  heaviest  payments  for  interest  and  the 
retirement  of  principal  must  be  made  in  the  early  years  of  the 
term  of  the  bonds,  before  the  work  for  which  they  pay  has  yielded 
any  returns.  Consequently  what  are  known  as  deferred  serial 
bonds  are  now  used  to  meet  such  conditions  as  often  arise  in 
road  districts.  With  such  a  type  of  bond,  no  principal  is  retired 
until  a  certain  period,  usually  five  years,  has  elapsed.  During 
this  period  interest  is  paid  but  nothing  more.  Thereafter  the 
principal  is  retired  by  uniform  amounts  and  the  interest  charges 
are  met  just  as  in  the  case  of  straight  serial  bonds  having  a  term 
shorter  by  five  years,  or  whatever  is  the  deferred  period.  In 
this  way  a  road  district  need  not  pay  anything  but  interest  until 

1  The  following  comment  on  this  type  of  bond  has  been  received  from 
John  S.  Harris,  of  the  banking  house  of  Sidney  Spitzer  and  Company, 
Toledo:  "We  would  not  suggest  your  recommending  the  installment 
(annuity)  bonds,  as  they  are  very  hard  to  figure  and  hard  to  dispose  of. 
It  is  necessary  to  figure  each  year  when  you  collect  your  coupons  the 
amount  of  principal  and  the  amount  of  interest.  A  serial  bond  answers 
the  same  purpose  and  is  much  more  attractive  to  the  investing  public. 
Road  bonds  should  not  be  issued  in  any  other  way  than  as  serial  bonds,  as 
every  one  knows  that  issuing  long-time  road  bonds  is  wrong." 


HIGHWAY   BONDS  183 

the  improvements  have  begun  to  yield  a  return  and  it  need  not 
pay  so  much  for  the  use  of  money  as  when  it  issues  sinking  fund 
bonds. 

The  question  which  taxpayers  generally  put  to  public  officials 
regarding  a  bond  issue  is  what  increase  such  an  issue  will  make  in 
the  annual  taxes.  A  series  of  examples  will  show  how  the  ac- 
companying tables  can  be  used  to  answer  such  questions. 

What  is  the  tax  rate  for  a  $300,000  issue  of  5  per  cent,  40-year 
bonds,  retired  by  a  sinking  fund  drawing  3  per  cent,  when  the 
tax  valuation  of  the  road  district  is  $9,300,000? 

The  table  of  the  annual  cost  of  sinking  fund  bonds  shows  that  the 
annual  cost  of  a  $1  bond  of  this  class  is  6.326  cents.  The  annual 
cost  of  a  $300,000  issue  will  be  $18,978.  The  additional  tax  per 
$100  valuation  in  the  district  will  be  $18,978  +  93,000  =  20.407 
cents.  Any  taxpayer  can  find  out  what  his  additional  tax  will 
be  by  multiplying  20.407  cents  by  the  number  of  hundreds  of 
dollars  worth  of  property  for  which  he  is  assessed.  If  his  prop- 
erty is  assessed  at  $2000,  for  example,  his  additional  tax  for 
roads  will  be  $4.08. 

How  much  money  would  be  saved  by  issuing  annuity  rather 
than  sinking  fund  bonds  in  this  case? 

The  annual  cost  of  a  1-dollar  4-per  cent,  40-year  annuity  bond 
is  shown  by  the  table  to  be  5.828  cents,  so  the  annual  cost  of  a 
$300,000  issue  will  be  $17,484.  The  additional  tax  per  $100 
valuation  will  be  18.8  cents,  or  1.607  cents  less  than  under  the 
sinking  fund  system.  The  man  whose  property  is  assessed  at 
$2000  would  save  32  cents,  and  the  district  as  a  whole  would 
save  $1494.51,  which  would  go  a  long  ways  toward  paying  for 
the  engineering  expenses  of  the  road  improvement. 

What  is  the  least  expensive  type  of  a  $300,000  issue  of  5  per 
cent,  40-year  bonds  to  the  above  district? 

The  four  accompanying  tables  show  that  the  straight  serial 
bond  is  the  least  expensive  type,  for  the  average  annual  cost  of 
a  1-dollar  bond  of  this  type  is  5.062  cents.  This  is  equivalent 
to  $15,186  for  a  $300,000  issue.  The  additional  tax  per  $100 
valuation  will  be  16.329  cents,  4.978  cents  less  than  under  the 
sinking  fund  type,  which  will  save  81  cents  to  the  man  having 
property  assessed  at  $2000.  The  saving  to  the  district  will  be 
$3792  as  compared  with  a  sinking  fund  issue  and  $2298  as  com- 
pared with  an  annuity  issue. 

The  drawback  of  a  straight  serial  bond  can  be  seen  from  the  fig- 
ures of  the  payment  needed  at  the  end  of  the  first  and  the  fortieth 
years,  7.5  and  2.625  cents  respectively  on  a  1-dollar  bond.  Road 
improvements  do  not  yield  any  benefits  until  completed,  and  by 
deferring  payment  on  the  principal  for  five  years,  the  additional 
cost  to  the  community  will  average  only  $939  a  year.  The 
maximum  annual  amount  will  be  somewhat  higher  than  in  a 


184  AMEHICAN   HIGHWAY  ASSOCIATION 

straight  40-year  serial  issue,  because  the  principal  must  be  re- 
tired in  35  years  instead  of  40  years,  but  this  disadvantage  may 
not  outweigh  the  desirability  of  deferring  the  repayment  of  the 
principal. 

The  management  of  a  bond  issue  requires  attention  to  all  the 
requirements  of  the  laws  governing  such  matters  and  a  knowledge 
of  the  conditions  which  affect  the  value  of  bonds.  Every  step 
which  the  law  requires  to  be  taken  in  connection  with  such  bonds 
must  not  only  be  taken  properly  but  recorded  fully  and  clearly. 
As  soon  as  the  voters  authorize  the  issue,  a  statement  of  the  fact 
should  be  drawn  up,  showing  also  the  area,  population  and  as- 
sessed valuation  of  the  district,  the  value  of  its  agricultural  and 
industrial  products,  its  material  resources  and  the  extent  of  their 
development,  the  banking  and  transportation  facilities  serving 
it,  the  existing  indebtedness  of  the  district,  the  condition  and 
number  of  the  schools,  and  all  other  information  which  will  indi- 
cate the  resources  and  character  of  the  community  that  has  de- 
cided to  borrow  the  money.  This  information  should  be  sent 
to  banking  houses  and  insurance  companies  making  a  specialty 
of  purchasing  public  bonds  and,  if  the  issue  is  a  large  one,  it 
should  be  advertised  in  financial  journals.  There  should  be 
ample  time  between  the  publication  of  these  notices  and  the  sale 
of  the  bonds  for  purchasers  to  make  a  full  investigation  of  them. 

1  Private  sales  of  bonds  for  public  works  should  be  discouraged 
all  sales  of  bonds  should  be  publicly  advertised,  and  bidders 
should  be  invited  to  submit  sealed  bids  on  or  before  a  certain 
date.  The  bonds  should  be  sold  to  the  highest  responsible  bid- 
der who  complies  with  all  of  the  terms  and  conditions  of  the  sale. 
The  city  or  county  should  reserve  the  right  to  reject  any  or  all 
of  the  bids,  as  a  protection  against  any  effort  to  pool  bids  and 
purchase  the  bonds  at  a  price  considerably  less  than  their  value. 

Some  cities  and  counties  engage  competent  attorneys,  familiar 
with  the  preparation  of  the  legal  papers  pertaining  to  bond  is- 
sues, to  examine  the  records  prior  to  the  sale  and  to  prepare  all 
necessary  forms.  The  city  or  county  assumes  the  expense  for 
all  such  work  and  furnishes  the  successful  bidder  with  the  approv- 
ing opinion  of  the  counsel  thus  engaged  and  with  the  executed 
bonds.  Some  cities  and  counties  go  even  further  by  providing 
uniform  proposal  blanks  for  the  bonds  and  refusing  to  accept  bids 
not  made  on  such  blank.  The  advantage  of  these  provisions  is 
that  the  seller  knows  he  is  offering  a  legally  and  validly  issued 
bond,  the  buyer  has  the  same  assurance,  and  the  value  of  the  is- 
sue is  certainly  enhanced  thereby.  The  seller  is  undoubtedly  re- 
imbursed for  the  expense  incurred  in  such  preparatory  work  by 
the  price  he  receives  for  the  bonds. 


and  the  next  paragraph  were    prepared    by  Baker,   Watts   & 
Company. 


Annual  cost  of  a  1-dollar   sinking-fund   bond  for  different  terms,  interest 
rates  and  rates  of  interest  on  sinking  fund 


INTER- 
EST ON 
SINK- 
ING 

FUND 

TERM 

RATE  OP  INTEREST  ON  BONDS,  PER  CENT 

4 

4.25 

4.5 

4.75 

5 

5.25 

5.5 

6 

percent 

years 

cents 

cents 

cents 

cents 

cents 

cents 

cents 

cents 

2 

5 

23.216 

23.466 

23.716 

23.966 

24.216 

24.466 

24.716 

25.216 

10 

13.133 

13.383 

13.633 

13.883 

14.133 

14.383 

14.633 

15.133 

15 

9.783 

10.033 

10.283 

10.533 

10.783 

11.033 

11.283 

11.783 

20 

8.116 

8.366 

8.616 

8.866 

9.116 

9.366 

9.616 

10.116 

25 

7.122 

7.372 

7.622 

7.872 

8.122 

8.372 

8.622 

9.122 

30 

6.465 

6.715 

6.965 

7.215 

7.465 

7.715 

7.965 

8.465 

35 

6.000 

6.250 

6.500 

6.750 

7.000 

7.250 

7.500 

8.000 

40 

5.656 

5.906 

6.156 

6.406 

6.656 

6.906 

7.156 

7.656 

45 

5.391 

5.641 

5.891 

6.141 

6.391 

6.641 

6.891 

7.391 

50 

5.182 

5.432 

5.682 

5.932 

6.182 

6.432 

6.682 

7.182 

2.5 

5 

23.023 

23.273 

23.523 

23.773 

24.023 

24.273 

24.523 

25.023 

10 

12.926 

13.176 

13.426 

13.676 

13.926 

14.176 

14.426 

14.926 

15 

9.577 

9.827 

10.077 

10.327 

10.577 

10.827 

11.077 

11.577 

20 

7.915 

8.165 

8.415 

8.665 

8.915 

9.165 

9.415 

9.915 

25 

6.928 

7.178 

7.428 

7.678 

7.928 

8.178 

8.428 

8.928 

30 

6.278 

6.528 

6.778 

7.028 

7.278 

7.528 

7.778 

8.278 

35 

5.821 

6.071 

6.321 

6.571 

6.821 

7.071 

7.321 

7.821 

40 

5.484 

5.734 

5.984 

6.234 

6.484 

6.734 

6.984 

7.484 

45 

5.227 

5.477 

5.727 

5.977 

6.227 

6.477 

6.727 

7.227 

50 

5.026 

5.276 

5.526 

5.776 

6.026 

6.276 

6.526 

7.026 

3 

5 

28.835 

23.085 

23.335 

23.585 

23.835 

24.085 

24.335 

24.835 

10 

12.723 

12.973 

13.223 

13.473 

13.723 

13.973 

14.223 

14.723 

15 

9.377 

9.627 

9.877 

10.127 

10.377 

10.627 

10.877 

11.377 

20 

7.722 

7.972 

8.222 

8.472 

8.722 

8.972 

9.222 

9.722 

25 

6.743 

6.993 

7.243 

7.493 

7.743 

7.993 

8.243 

8.743 

30 

6.102 

6.352 

6.602 

6.852 

7.102 

7.352 

7.602 

8.102 

35 

5.654 

5.904 

6.154 

6.404 

6.654 

6.904 

7.154 

7.654 

40 

5.326 

5.576 

5.826 

6.076 

6.326 

6.576 

6.826 

7.326 

45 

5'.  079 

5.329 

5.579 

5.829 

6.079 

6.329 

6.579 

7.079 

50 

4.887 

5.137 

5.387 

5.637 

5.887 

6.137 

6.387 

6.887 

3.5 

5 

22.648 

22.898 

23.148 

23.398 

23.648 

23.898 

24.148 

24.648 

10 

12.524 

12.774 

13.024 

13.274 

13.524 

13.774 

14.024 

14.524 

15 

9.183 

9.433 

9.683 

9.933 

10.183 

10.433 

10.683 

11.183 

20 

7.536 

7.786 

8.036 

8.286 

8.536 

8.786 

9.036 

9.536 

25 

6.567 

6.817 

7.067 

7.317 

7.567 

7.817 

8.067 

8.567 

30 

5.937 

6.187 

6.437 

6.687 

6.937 

7.187 

7.437 

7.937 

35 

5.500 

5.750 

6.000 

6.250 

6.500 

6.750 

7.000 

7.500 

40 

5.183 

5.433 

5.683 

5.933 

6.183 

6.433 

6.683 

7.183 

45 

4.945 

5.195 

5.445 

5.695 

5.945 

6.195 

6.445 

6.945 

50 

4.763 

5.013 

5.263 

5.513 

5.763 

6.013 

6.263 

6.763 

1 

4 

5 

22.463 

22.713 

22.963 

23.213 

23.463 

23.713 

23.963 

24.463 

10 

12.329 

12.579 

12.829 

13.079 

13.329 

13.579 

13.829 

14.329 

15 

8.994 

9.244 

9.494 

9.744 

9.994 

10.244 

10.494 

10.994 

20 

7.358 

7.608 

7.858 

8.108 

8.358 

8.608 

8.858 

9.358 

25 

6.401 

6.651 

6.901 

7.151 

7.401 

7.651 

7.901 

8.401 

30 

5.783 

6.033 

6.283 

6.533 

6.783 

7.033 

7.283 

7.783 

35 

5.358 

5.608 

5.858 

6.108 

6.358 

6.608 

6.858 

7.358 

40 

5.052 

5.302 

5.552 

5.802 

6.052 

6.302 

6.552 

7.052 

45 

4.826 

5.076 

5.326 

5.576 

5.826 

6.076 

6.326 

6.826 

50 

4.655 

4.905 

5.155 

5.405 

5.655 

5.905 

6.155 

6.655 

185 


186 


AMERICAN   HIGHWAY   ASSOCIATION 


Annual  cost  of  a  1-dollar  sinking-fund  bond  for  different  terms,  interest 
rates  and  rates  of  interest  on  sinking  fund — Continued 


INTER- 
EST   ON 

RATE   OP  INTEREST   ON   BONDS,   PER  CENT 

SINK- 
ING 
FUND 

TERM 

4 

4.25 

4.5 

4.75 

5 

5.25 

5.5 

6 

per  cent 

years 

cents 

cents 

cents 

cents 

cents 

cents 

cents 

cents 

4.5 

5 

22.279 

22.529 

22.779 

23.029 

23.279 

23.529 

23.779 

24.279 

10 

12.138 

12.388 

12.638 

12.888 

13.138 

13.388 

13.638 

14.138 

15 

8.811 

9.061 

9.311 

9.561 

9.811 

10.061 

10.311 

10.811 

20 

7.188 

7.438 

7.688 

7.938 

8.188 

8.438 

8.688 

9.188 

25 

6.244 

6.494 

6.744 

6.994 

7.244 

7.494 

7.744 

8.244 

30 

5.639 

5.889 

6.139 

6.389 

6.639 

6.889 

7.139 

7.639 

35 

5.227 

5.477 

5.727 

5.977 

6.227 

6.477 

6.727 

7.227 

40 

4.934 

5.184 

5.434 

5.684 

5.934 

6.184 

6.434 

6.934 

45 

4.720 

4.970 

5.220 

5.470 

5.720 

5.970 

6.220 

6.720 

50 

4.560 

4.810 

5.060 

5.310 

5.560 

5.810 

6.060 

6.560 

Annual  cost  of  a  1-dollar  annuity  bond  for  different  terms  and  rates  of  interest 


RATE   OF  INTEREST  ON   BONDS,   PER  CENT 


4 

4.25 

4.5 

4.75 

5 

5.25 

5.5 

6 

r«or« 

cents 

cents 

cents 

cents 

cents 

cents 

cents 

centt 

5 

22.462 

22.621 

22.779 

22.938 

23.097 

23.257 

23.418 

23.740 

10 

12.329 

12.483 

12.638 

12.794 

12.950 

13.108 

13.267 

13.587 

15 

8.994 

9.152 

9.311 

9.472 

9.634 

9.798 

9.963 

10.296 

20 

7.358 

7.522 

7.688 

7.855 

8.024 

8.195 

8.368 

8.718 

25 

6.401 

6.571 

6.744 

6.919 

7.095 

7.274 

7.455 

7.823 

30 

5.783 

5.960 

6.139 

6.321 

6.505 

6.692 

6.880 

7.265 

35 

5.358 

5.541 

5.727 

5.916 

6.107 

6.301 

6.497 

6.897 

40 

5.052 

5.242 

5.434 

5.630 

5.828 

6.029 

6.232 

6.646 

45 

4.826 

5.022 

5.220 

5.422 

5.626 

5.833 

6.043 

6.470 

50 

4.655 

4.856 

5.060 

5.267 

5.478 

5.691 

5.906 

6.344 

HIGHWAY   BONDS 


187 


Variations  in  annual  cost  of  a  1 -dollar  serial  bond  for  different  terms  and 

rates  of  interest,  the  principal  being  retired  by  the  same  amount  at  the 

end  of  each  year 


TERM 

PAYMENT 

RATE   OP  INTEREST,  PER  CENT 

4 

4.25 

4.5 

4.75 

5 

5.25 

5.5 

6 

years 

5 

10 
15 
20 
25 
30 
35 
40 
45 
60 

date 

First  year  
Last  year  

cents 

24.000 
20.800 
22.400 

14.000 
10.400 
12.200 

10.667 
6.933 
8.800 

.9.000 
5.200 
7.100 

8.000 
4.160 
6.080 

7.333 
3.467 
5.400 

6.857 
2.971 
4.914 

6.500 
2.600 
4.550 

6.222 
6.311 
4.267 

6.000 
2.080 
4.040 

cents 

24.250 
20.850 
22.550 

14.250 
10.425 
12.337 

10.917 
6.950 
8.933 

9.250 
5.213 
7.231 

8.250 
4.170 
6.210 

7.583 
3.475 
5.530 

7.107 

2.978 
5.047 

6.750 
2.606 
4.678 

6.472 
3.316 
4.394 

6.250 
2.085 
4.167 

cents 

24.500 
20.900 
22.700 

14.500 
10.450 
12.475 

11.167 
6.967 
9.067 

9.500 
5.225 
7.362 

8.500 
4.180 
6.340 

7.833 
3.483 
5.658 

7.357 
2.985 
5.171 

7.000 
2.613 
4.806 

6.722 
2.322 
4.522 

6.500 
2.090 
4.295 

cents 

24.725 
20.950 
22.850 

14.750 
10.475 
12.613 

11.417 

6.984 
9  200 

9.750 
5.238 
7.494 

8.750 
4.190 
6.470 

8.083 
3.491 

5.787 

7.607 
2.993 
5.300 

7.250 
2.619 
4.934 

6.972 
2.328 
4.650 

6.750 
2.095 
4.427 

cents 

25.000 
21.000 
23.000 

15.000 
10.500 
12.750 

11.667 
7.000 
9.333 

10.000 
5.250 
7.625 

9.000 
4.200 
6.600 

8.333 
3.500 
5.916 

7.857 
3.000 

5.428 

7.500 
2.625 
5.062 

7.222 
2.333 

4.777 

8.000 
2.100 
4.550 

cents 

25.250 
21.050 
23.150 

15.250 
10.525 

12.888 

11.917 

7.017 
9.467 

10.250 
5.263 
7.756 

9.250 
4.210 
6.730 

8.583 
3.509 
6.046 

8.107 
3.007 
5.557 

7.750 
2.632 
5.191 

7.472 
2.339 
4.905 

7.250 
2.105 
4.677 

cents 
25.500 
21.100 
23.300 

15.500 
10.550 
13.025 

12.167 
7.034 
9.600 

10.500 
5.275 

7.887 

9.500 
4.220 
6.810 

8.833 
3.517 
6.175 

8.357 
3.014 
5.685 

8.000 
2.640 
5.320 

7.722 
2.344 
5.033 

7.500 
2.110 
4.805 

cents 

26.000 
21.200 
23.600 

16.000 
10.600 
13.300 

12.667 
7.067 
9.867 

11.000 
5.287 
8.144 

10.000 
4.240 
7.120 

9.333 
3.535 
6.434 

8.857 
3.028 
5.942 

8.500 
2.654 
5.577 

8.222 
2.355 
5.288 

8.000 
2.120 
6.060 

Average  . 

First  year.  .  .  . 

Last  year  

Average 

First  year. 

Last  year 

Average.. 

First  year  

Last  year.  .  . 

Average 

First  year  
Last  year  

Average.. 

First  year. 

Last  year 

Average...  . 

First  year  
Last  year  

Average 

First  year  
Last  year  
Average.. 

First  year  
Last  year  
Average  

First  year  
Last  year  
Average..  . 

188 


AMERICAN   HIGHWAY   ASSOCIATION 


Variations  in  annual  cost  of  a  1-dollar  deferred  serial  bond  for  different 
terms  and  rates  of  interest,  the  principal  being  retired  by  the  same  amount 
at  the  end  of  each  year  beginning  with  the  end  of  the  sixth  year 


TERM 

PAYMENT 

RATE   OF  INTEREST,  PER  CENT 

4 

4.25 

4.5 

4.75 

5 

5.25 

5.5 

6 

years 

10 
15 
20 
25 
30 
35 
40 
45 
50 

date 

1-5  years  
Sixth  year  
Last  year 

cents 
4.000 

24.000 
20.800 
13.200 

cents 

4.250 
24.250 
20.850 
13.400 

4.250 
14.250 
10.425 
9.641 

4.250 
10.917 
6.950 
7.762 

4.250 
9.250 
5.213 
6.635 

4.250 
8.250 
4.170 

5.883 

4.250 
7.583 
3.475 
5.347 

4.250 
7.107 
2.978 
4.947 

4.250 
6.750 
2.606 
4.630 

4.250 
6.472 
2.316 
4.380 

cents 

4.500 
24.500 
20.900 
13.600 

4.500 
14.500 
10.450 
9.817 

4.500 
11.167 
6.967 
7.925 

4.500 
9.500 
5.225 
6.790 

4.500 
8.500 
4.180 
6.033 

4.500 
7.833 
3.483 
5.492 

4.500 
7.357 
2.985 
5.087 

4.500 
7.000 
2.613 

4.772 

4.500 
6.722 
2.322 
4.720 

cents 

4.750 
24.725 
20.950 
13.800 

4.750 
14.750 
10.475 
9.992 

4.750 
11.417 
6.984 
8.088 

4.750 
9.750 
5.238 
6.945 

4.750 
8.750 
4.190 
6.183 

4.750 
8.083 
3.491 
5.639 

4.750 
7.607 
2.993 
5.231 

4.750 
7.250 
2.619 
4.914 

4.750 
6.972 
2.328 
4.385 

cents 

5.000 
25.000 
21.000 
14.000 

5.000 
15.000 
10.500 
10.166 

5.000 
11.667 
7.000 
8.250 

5.000 
10.000 
5.250 
7.100 

5.000 
9.000 
4.200 
6.333 

5.000 
8.333 
3.500 
5.785 

5.000 
7.857 
3.000 
5.375 

5.000 
7.500 
2.625 
5.055 

5.000 
7.222 
2.333 
4.799 

cents 

5.250 
25.250 
21.050 
14.275 

5.250 
15.250 
10.525 
10.342 

5.250 
11.917 
7.017 
8.413 

5.250 
10.250 
5.263 
7.255 

5.250 
9.250 
4.210 
6.483 

5.250 
8.583 
3.509 
5.932 

5.250 
8.107 
3.007 
5.519 

5.250 
7.750 
2.632 
5.198 

5.250 
7.472 
2.339 
4.415 

cents 

5.500 
25.500 
21.100 
14.400 

5.500 
15.500 
10.550 
10.516 

5.500 
12.167 
7.034 
8.575 

5.500 
10.500 
5.275 
7.410 

5.500 
9.500 
4.220 
6.592 

5.500 
8.833 
3.517 
6.079 

5.500 
8.357 
3.014 
5.662 

5.500 
8.000 
2.640 
5.340 

5.500 
7.722 
2.344 
4.530 

cents 

6.000 
26.000 
21.200 
14.800 

6.000 
16.000 
10.600 
10.867 

6.000 
12.667 
7.067 
8.900 

6.000 
11.000 
5.287 
7.715 

6.000 
10.000 
4.240 
5.933 

6.000 
9.333 
3.535 
6.372 

6.000 
8.857 
3.028 
5.199 

6.000 
8.500 
2.654 
5.624 

6.000 
8.222 
2.355 
4.759 

Average.. 

1-5  years  
Sixth  year  
Last  year 

4.000 
14.000 
10.400 
9.467 

4.000 
10.667 
6.933 
7.600 

4.000 
9.000 
5.200 
.6.480 

4.000 
8.000 
4.160 
5.733 

4.000 
7.333 
3.467 
5.200 

4.000 
6.857 
2.971 
4.800 

4.000 
6.500 
2.600 
4.489 

4.000 
6.222 
2.311 
4.240 

Average.. 

1—5  years 

Sixth  year  
Last  year  

Average.. 

1—5  years.  .  .  . 

Sixth  year  
Last  year.  .  . 

Average  

1—5  years.. 

Sixth  year  
Last  year 

Average  
1—5  years  

Sixth  year  
Last  year  
Average.. 

1—5  years... 

Sixth  year.  ... 
Last  year  
Average 

1-5  years  
Sixth  year  
Last  year  
Average  

1—5  years 

Sixth  year  
Last  year  
Average..  . 

RESISTANCE  OF  ROADS  TO  TRACTION 

The  resistance  to  traction  of  a  small  number  of  pavements  of 
different  types,  in  different  conditions  was  investigated  in  1915 
by  the  electrical  engineering  department  of  the  Massachusetts 
Institute  of  Technology.  A  half-ton  electric  delivery  wagon  was 
used,  and  each  test  was  made  by  driving  the  wagon  over  the  test 
pavement  in  one  direction  and  then  in  the  other,  so  that  the  ef- 
fect of  the  wind,  if  any,  would  be  neutralized  by  averaging  the 
results  of  the  runs  in  both  directions.  The  tests  are  described  in 
a  paper  presented  to  the  American  Institute  of  Electrical  Engi- 
neers in  June,  1916,  by  Profs.  A.  E.  Kennelly  and  O.  R.  Schurig. 
The  results  were  summarized  in  the  accompanying  illustration. 

Curve  1  is  nearly  flat,  and  the  authors  state  that  if  the  effect 
of  air  resistance  was  eliminated  from  the  total  resistance  to  trac- 
tion, the  resistance  of  a  good  level  asphalt  pavement  would  be 
about  17  pounds  per  ton  at  all  speeds.  Such  a  pavement  in 
poor  condition  had  a  resistance  of  about  23  pounds  per  ton  when 
the  wagon  ran  at  12  miles  per  hour  and  25  pounds  at  15  miles. 
There  were  no  tests  of  wood  block  pavements  in  poor  condition; 
curve  2  gives  the  results  for  a  good  pavement. 

Curve  3  is  for  a  good  brick  pavement;  the  effect  of  slight  wear 
of  bricks  was  to  increase  the  tractive  resistance  to  25  pounds  per 
ton  at  12  miles  and  about  30  pounds  at  15  miles. 

Curve  4  is  for  a  dry,  hard  water-bound  macadam  road  in  fair 
condition.  A  similar  road  in  a  dusty  condition  showed  an  in- 
crease of  3  pounds  in  the  resistance  to  traction  at  all  speeds.  A 
poor,  damp  road  in  poor  condition  offered  a  resistance  of  33 
pounds  at  10  miles  and  39  pounds  at  13  miles.  Oiling  a  good 
water-bound  macadam  road  increased  its  resistance  to  traction 
about  5  pounds,  this  increase  gradually  growing  larger  as  the 
speed  increased. 

Curve  5  is  for  bituminous  macadam  in  good  condition.  The 
curve  for  another  road  in  good  condition  began  with  a  resistance 
of  a  little  under  26  pounds  per  ton  at  9  miles  an  hour  and  in- 
creased to  32  pounds  at  14  miles.  AJI  old  road  of  this  type  in 
poorly  patched  condition  offered  a  resistance  of  about  29  pounds 
at  8  miles  and  37  pounds  at  13  miles.  A  good  road  which  was 
recently  treated  and  still  soft  had  a  resistance  of  33  pounds  at  8 
miles  and  nearly  36  pounds  at  13  miles,  as  shown  in  Curve  9. 
A  very  poor,  soft  road  with  many  holes  had  a  resistance  of  41 

189 


190 


AMERICAN  HIGHWAY   ASSOCIATION 


pounds  at  7  miles  and  54  pounds  at  12  miles,  showing  what  a 
rapid  increase  to  resistance  follows  an  attempt  to  go  at  even 
moderate  speed  over  such  a  road. 

The  authors  make  the  following  comments  of  the  tests: 
There  are  three  principal  elements  which  determine  the  trac- 
tive-resistance curve  for  different  speeds  and  a  given  vehicle,  within 
the  range  of  conditions  covered  by  the  tests. 

The  first  element  is  a  constant  resistance,  the  magnitude  of 
which  depends  on  the  lack  of  resilience  of  the  road  surface  and 
the  tires,  that  is  to  say,  on  the  energy  losses  due  to  displacement 
of  tire  material  and  road-surface  material.  This  constant  ele- 


(22      44 


14 


16      18      20 
SPEED- KM.  PER  HR. 
10     11     12     13 
SPEED -MILES  PER  HR. 


8  i  10          il          12  13  fc  l'5  1*6 

CURVES  SHOWING  RESISTANCE  TO  TRACTION  AT  DIFFERENT  SPEEDS 


ment  would  be  encountered  upon  a  smooth,  level  road  of  the 
particular  type  considered,  in  the  absence  of  impact,  air  and  wind 
resistance. 

The  second  element  is  an  increasing  resistance  with  increasing 
speed  due  to  impact  losses.  This  resistance  results  from  lack  of 
smoothness  of  the  road  surface  and  varies  approximately  as  the 
second  power  of  the  velocity  at  impact. 

The  third  element  is  an  increasing  resistance  with  increased 
speed.  It  is  due  to  the  air  pressure  against  the  front  of  the 
vehicle  and  varies  approximately  as  the  second  power  of  the 
speed. 


RESISTANCE    OF   ROADS    TO    TRACTION  191 

The  first  element  is  called  the  displacement  resistance,  the  second 
the  impact  resistance  and  the  third  the  air  resistance.  The 
displacement  resistance  is  very  marked  in  Curve  10,  for  a  granite- 
block  pavement  with  sand  joints.  The  displacement  resist- 
ance varies,  not  only  with  the  type  and  surface  quality  of  the 
road,  but  also  with  the  type,  dimensions  and  quality  of  the  tires 
on  the  wheels.  The  same  tires  were  used  in  the  experiments  by 
Kennelly  and  Schurig.  The  air  resistance  of  a  given  vehicle  at 
any  given  speed  is  the  same  for  all  classes  of  pavement.  The 
impact  resistance  of  a  road  depends  not  only  on  the  type  and 
character  of  the  road  surface  and  the  sizes  of  its  irregularities, 
but  also  on  the  type,  dimensions  and  quality  of  the  tires  on  the 
wheels,  the  weight  of  the  truck  and  the  quality  of  its  springs. 

Increasing  the  gross  weight  of  the  vehicle  by  12  per  cent, 
through  load,  was  found  to  have  no  effect  on  tractive  resistance 
within  the  observed  speed  limits  for  smooth  roads  in  good  con- 
dition; but  on  rough  roads,  a  distinct  increase  in  tractive  resist- 
ance with  this  extra  weight  was  observed. 


RURAL  PUBLIC  ROADS  OF  UNITED  STATES 
AT  CLOSE  OF  1915 

Circular  68,   United  States    Department  of   Agriculture.    Prepared  by  the 

Division  of  Road  Economics,  Office  of  Public  Roads  and  Rural 

Engineering. 


STATE 

TOTAL 
RURAL 
ROADS 

TOTAL 
SURFACED 
ROADS 

PERCENTAGE 
OF  ROADS 

SURFACED 

CASH 
EXPENDITURES 
FOR  ROADS 
IN  1915 

TOTAL  STATE 
FUNDS 
FOR  ROADS  TO 
JANUARY  1, 
1916 

Alabama  

miles 

55,446 

miles 

5,915 

10.7 

$4,283,207 

$586,405 

Arizona 

12,075 

350 

2.9 

1,076,178 

1  039  388 

Arkansas 

50,743 

1,200 

2.3 

2,803,000 

165  000 

California 

61,038 

13,000 

21.3 

20,753,281 

16,571  091 

Colorado  .       .  .       ... 

39,691 

1,750 

4.4 

2,193,000 

1,024,751 

Connecticut  

14,061 

3,200 

22.7 

3,484,944 

17,019,120 

Delaware  

3,674 

300 

8.0 

397,500 

224,695 

Florida 

17,995 

3,500 

19.4 

5,501,135 

1  135 

Georgia 

84,770 

13,000 

15.3 

3,700,000 

Idaho. 

23,109 

950 

4.1 

1,974,636 

572  812 

Illinois.  ...       

94,141 

11,000 

11.7 

9,263,995 

1  686  627 

Indiana  

63,370 

27,000 

42.6 

13,000,000 

Iowa  

106,847 

1,000 

1.0 

13,606,299 

255,935 

Kansas 

111,536 

1,250 

1.1 

5,510,000 

30  000 

Kentucky  

57,916 

13,000 

22.1 

3,122,430 

616,715 

Louisiana 

24,562 

2,250 

9.1 

3,569,709 

606  327 

Maine  .  .  . 

25,528 

3,000 

11.7 

3,293,902 

5  865  209 

Maryland 

16,458 

2,950 

17.9 

5,630,000 

17,583,142 

Massachusetts  

18,681 

8,800 

46.6 

6,557,279 

18,999,992 

Michigan  

74,089 

8,600 

11.6 

10,174,738 

3,182,701 

Minnesota  

93,500 

5,500 

5.9 

8,292,000 

4,288,174 

Mississippi  

45,778 

2,500 

5.5 

2,900,000 

Missouri 

96,124 

8,000 

8.3 

8,369,189 

1  791  172 

Montana 

39,204 

775 

2.0 

3,676,318 

34346 

Nebraska  

80,338 

500 

0.6 

3,520,000 

377,850 

Nevada  . 

15,000 

75 

0.5 

250,000 

20,000 

New  Hampshire  

14,020 

1,800 

12.8 

2,363,414 

3,259,789 

New  Jersey  

14,817 

4,600 

31.0 

7,163,584 

8,355,576 

New  Mexico  

11,873 

450 

3.8 

584,919 

662,955 

New  York  

80,112 

17,500 

21.8 

24,255,648 

96,622,498 

North  Carolina  
North  Dakota 

50,758 
68,000 

6,500 
1,100 

12.8 
1.6 

5,510,000 
2,500,700 

38,500 

Ohio  

86,453 

30,920 

35.8 

12,975,688 

8,566,275 

Oklahoma.  .  .       ... 

107,916 

300 

0.3 

3,410,000 

30,323 

Oregon  

36,819 

7,780 

21.1 

6,182,000 

418,975 

Pennsylvania  

91,556 

9,883 

10.8 

12,541,257 

30,801,211 

Rhode  Island  

2,121 

1,246 

58.8 

594,119 

3,907,784 

South  Carolina 

42,220 

3,500 

8.3 

1,000,000 

South  Dakota 

96,306 

850 

0.9 

1,450,000 

Tennessee 

46,050 

8,625 

18.7 

3,503,500 

3,500 

Texas  

128,960 

12,000 

9.3 

9,500,000 

Utah  

15,000 

1,053 

7.0 

1,213,100 

809,732 

Vermont  

15,082 

3,478 

23.1 

1,475,145 

3,671,564 

Virginia 

53,388 

4,760 

8.9 

4,018,399 

2,713,550 

Washington  

42,428 

5,460 

12.8 

6,670,702 

8,552,789 

West  Virginia 

32,024 

1,200 

3.7 

2,759,212 

1  130,  978 

Wisconsin.  . 

75,702 

14,050 

18.5 

9,960,980 

4,219,001 

Wyoming  .  .  . 

14,381 

500 

3.5 

441,291 

43,237 

Total. 

2,451,660 

276,920 

11.3 

$266,976,399 

$265,350,824 

1  Of  this  $118,000  was  returned  to  the  counties  in  1911  by  act  of  legislature. 

192 


REVENUES  USED  IN  1914  IN  EACH  STATE  FOR 
PUBLIC  ROAD  AND  BRIDGE  PURPOSES  AND 
TOTAL  OUTSTANDING  BONDS  FOR  ROADS 
AND  BRIDGES  AT  CLOSE  OF  1914 

From  Bulletin  890,  U.  S.  Department  of  Agriculture,   Prepared  by  the  Office 
of  Public  Roads  and  its  State  Collaborators 


STATE 

PUBLIC  ROAD  AND  BRIDGE  REVENUES 

TOTAL  STATE  AND 
LOCAL  BONDS 

Total 

'Sj'ei 

Is 

£ 

l| 
%3 
PH 

Per  capita 

Per  $100 
assessed 
valuation 

Alabama  

$3,949,019.00 
982,721.22 
1,522,696.20 
19,171,984.66 
1,937,546.23 
3,640,962:75 
511628.00 
2,280,255.09 
3,688,172.25 
1,371,468.58 
8,734,712.77 
14,233,985.93 
10,187,507.32 
5,544,048.00 
2,474,621.00 
1,777,572.12 
2,642,006.79 
6,000,652.03 
6,091,875.30 
9,261,998.00 
6,458,940.07 
3,960,377.00 
5,513,048.71 
2,888,400.61 
1,796,277.69 
245,013.65 
1,590,464.11 
7,308,287.08 
556,398.82 
23,231,964.02 
5,2^5,490.78 
2,402,383.52 
14,3341245.98 
2*112,680.80 
5,310,466.76 
10,424,580.00 
446,496.05 
1,024,480.37 
1,217,809.42 
2,370,560.16 
9,920,079.11 
803,070.63 
1,023,941.01 
3,224,528.82 
7,944,717.38 
2,483,747.00 
9,880,240.50 
669,661.16 

$71.22 
81.38 
30.00 
314.09 
48.70 
258.90 
139.25 
126.71 
45.72 
56.22 
91.32 
194.06 
97.88 
49.92 
42.52 
72.37 
112.35 
364.60 
326.08 
124.84 
69.06 
86.51 
57.40 
73.67 
22.37 
20.11 
113.44 
486.49 
46.86 
2Q2.60 
102.75 
34.92 
165.99 
19.57 
144.23 
113.86 
205.76 
24.26 
12.64 
51.48 
76.92 
91.15 
71.86 
60.39 
187.25 
77.55 
130.50 
44.06 

$77.01 
8.63 
28.99 
123.17 
18.69 
755.50 
2£0.37 
41.56 
62.80 
16.45 
155.85 
394.89 
183.27 
67.79 
61.58 
39.10 
88.37 
603.62 
758.00 
161.13 
79.88 
85.42 
80.22 
19.75 
23.38 
2.23 
176.11 
959.00 
4.54 
467.00 
107.00 
34.23 
351.84 
30.45 
55.54 
232.00 
418.50 
33.59 
15.84 
56.86 
37.80 
9.77 
112.22 
80.08 
118.87 
103.39 
178.81 
6.86 

$1.840 
4.810 
0.960 
8.060 
2.420 
3.260 
2.520 
3.020 
1.410 
4.210 
1.540 
5.270 
4.580 
3.280 
1.080 
1.073 
3.550 
4.630 
1.810 
3.290 
3.110 
2.300 
1.670 
7.680 
1.510 
2,900 
3.690 
2.830 
1.690 
2.54Q 
2.360 
4.160 
3.000 
1.274 
7.890 
1.360 
0.820 
0.670 
2.080 
1.080 
2.540 
2.150 
2.870 
1.560 
6.950 
2.030 
4.230 
4.590 

$0.6900 
0.7000 
0.3600 
0.6600 
0.4600 
0.3500 
0.5450 
1.0700 
0.4370 
0.8200 
0.3700 
0.7500 
1.1300 
0.2000 
0.2390 
0.3220 
0.6330 
0.4850 
0.1270 
0.4000 
0.4400 
0.9620 
0.3000 
0.8300 
0.3900 
0.2400 
0.3620 
0.2£90 
0.7700 
0.2030 
0.6970 
0.6800 
0.2200 
0.1769 
0.5900 
0.2050 
0.0720 
0.3510 
0.3400 
0.3780 
0.3910 
0.4000 
0.4620 
0.3720 
0.7900 
0.2120 
0.4000 
0.3700 

$5,418,000.00 
295,000.00 
1,467,066.00 
32,277,000.00 
90,500.00 
7000000.00 
1  280000.00 
5959  199.00 
127500.00 
1,339,000.09 
798,761.55 
42,095,357.34 
1,960,780.00 

Arizona 

Arkansas  
California.. 

Colorado  
Connecticut  
Delaware  
Florida  

Georgia  

Idaho  
Illinois  

Indiana 

Iowa 

Kansas              .  . 

Kentucky. 

705,000.00 
1,588,835.00 
785,000.00 
12*863,700.00 
10,305,522.82 
10,389,029.43 
1,411,889.00 
8,327,172.00 
522,500.00 
2,224,050.72 

Louisiana    

Maine  

Maryland  
Massachusetts.  .  . 
Michigan  

Minnesota  

Mississippi 

Missouri  
Montana. 

Nebraska  
Nevada  
New  Hampshire.  . 
New  Jersey  

38,000.00 
675,000.00 
14,011,337.00 
157,000.00 
76,82^,088.00 
8,955,300.00 

New  Mexico  

New  York  

North  Carolina.. 
North  Dakota.... 
Ohio  
Oklahoma  
Oregon 

31,175,968.53 
1,440,000.00 
1,615,000.00 
127,547,659.00 
1,800,000.00 
460,000.00 

Pennsylvania  
Rhode  Island  
South  Carolina... 
South  Dakota  — 
Tennessee  
Texas  
Utah 

6,898,277.00 
14,615,017.00 
541,500.00 

5,650,994.93 
1,555,000.00 
1,303,000.00 
281,078.00 

Vermont  

Virginia  
Washington 

West  Virginia  
Wisconsin. 

Wyoming  

Total  or  ave  .  .  . 

$240,263,784.46 

$98.22 

$80.79 

$2.620 

$0.3500 

$344,763,082.32 

193 


EXTENT  OF  SURFACED  ROADS  IN  THE  UNITED 
STATES  AT  THE  CLOSE  OF  1914 

From  Bulletin  890,  U.  S.  Department  of  Agriculture,  Prepared  by  the  Office  of 
Public  Roads  and  its  State  Collaborators 


STATE 

MACADAM 

BITUMI- 
NOUS 
MACADAM 

GRAVEL 

SAND 
CLAY 

BRICK 

CON- 
CRETE 

MISCEL- 
LANEOUS 

TOTAL 
SURFACED 

miles 

4,988.50 
253.43 
1,097.50 
10,279.73 
1,193.87 
2,975.45 
243.50 
2,830.47 
12,342.12 
679.00 
11,606.31 
30,962.40 
614.57 
1,148.85 
12,403.28 
2,067  62 
2,762.36 
2,489.26 
8,505.89 
7,828.51 
3,967.83 
2,133.35 
6,712.57 
609.25 
1,204.54 
262.00 

1,659.63 
5,897.46 
261.50 
15,635.90 
6,003.75 
955.00 
30,569.17 
121.60 
4,726.40 
982.88 
693.42 
3,270.50 
363.00 
8,102.00 
10,526.79 
1,253.75 
1,442  03 
3,909.57 
4,922.09 
1,064.97 
13,399.47 
468.50 

Alabama 

miles 

431.00 
11.23 
362.50 
837.40 
3.00 
923.42 
161.50 
829.16 
234.00 
42.50 
1,675.11 
10,291.29 
171.30 
194.30 
10,628.00 

miles 

31.00 
13.50 
4.00 
877.90 

'"i28;28 
35.50 
42.80 
87.00 
12.00 
121.53 
168.35 

'"59  '.03 

miles 

2,589.50 
125.70 
535.00 
3,563.59 
574.25 
1,057.93 
21.00 
42.50 
1,073.00 
168.00 
7,052.30 
20,264.59 
413.00 
151.85 
1,713.50 
430.00 
1,139.36 
243.95 
6,289.57 
5,230.25 
2,825.25 
1,281.10 
3,671.50 
514.25 
21.00 
193.00 

1,013.70 
2,858.52 
184.00 
5,802.97 
529.00 
955.00 
15,385.93 
6.90 
3,060.15 
•235.19 
230.10 
85.00 
212.00 
2,788.00 
5,258.98 
685.75 
1,165.42 
822.09 
3,924.48 
20.50 
9,597.00 
52.50 

miles 
1,916.00 
45.00 
175.00 
582.25 
450.12 
840.27 

T,i63!66 
10,778.00 
449.00 
2,467.95 
150.25 
23.00 
758.50 

"i',44^66 
2.26 
69.00 

miles 

miles 
1.00 

miles 
20.00 
58.00 

"3,  489!  46 
164.25 

Arizona  
Arkansas 

21.00 
929.19 
2.25 
24.22 

'"i2!66 
.40 
4.50 
148.80 
53.17 
5.77 
1.35 
2.50 

California  
Colorado 

'"iis's 

'256!  24 
1.72 

"'82i92 
34.75 

'"i'.io 

.25 

Connecticut  
Delaware  
Florida. 

25.50 
484.77 
168.00 
3.00 
57.70 

'"ilso 

38.75 

'"i89'62 
1,510.89 
455.96 
44.69 

Georgia 

Idaho- 

Illinois  

Indiana  
Iowa  

Kansas  

Kentucky  
Louisiana.. 

Maine  
Maryland..  .  . 

55.36 
488.70 
834.30 
1,021.19 
120.25 
86.00 
1,531.05 
78.00 
39.21 
2.00 

61.87 
1,809.24 

5,7i7!97 
1,111.00 

12,903  '87 
6.70 
1,000.72 
*  1,881.  80 
352.92 
27.50 

43.93 
1,042.31 
1,337.33 
94.50 
19.00 
29.58 
59.00 

.05 

10.51 
189.34 

Massachusetts.. 
Michigan  
Minnesota  
Mississippi  
Missouri.  . 

1,375.27 
985.33 
604.25 
1,442.25 
14.00 
1,131.10 
67.00 

270.90 
561.40 
72.50 

'  '  '  .'50 

107.30 
17.50 
14.00 
2.77 

118.50 
5.00 
3.00 
2.00 

1.00 

Montana  . 

Nebraska  
Nevada.. 

1.30 

2.40 

7.53 

New  Hamp- 
shire   
New  Jersey  
New  Mexico  
New  York  
North  Carolina. 
North  Dakota.. 
Ohio- 

154.26 
417.63 
5.00 
3,168.63 
9.00 

"i',066'.29 
3.00 
137.25 
•198.33 
107.40 
3.50 
10.00 
148.00 
181.00 
15.50 

'    '255!  77 
165.52 
62.95 
183.00 

7.07 

151.83 
250.67 

148.53 

244.19 
1.25 

553.61 
40.00 

4,313.50 

211.00 
105.00 
300.00 

640.41 

315.67 

46.00 

Oklahoma  
Oregon  
Pennsylvania... 
Rhode  Island... 
South  Carolina. 
South  Dakota.. 
Tennessee  
Texas  
Utah  
Vermont  
Virginia 

'"•269  '.33 

28.41 

199.87 
7,398.23 
3.00 
53.50 
12.00 

ii674.08 

3,101.00 
129.00 
613.00 
3,490.48 
401.00 

4,550.50 
511.00 
49.00 
1.94 
1,177.89 
502.82 
771.92 
1,408.00 

.50 

2.00 
11.25 
2.50 



274.67 
142.17 
140.00 
70.00 
72.00 
416.00 

1,511.65 
83.50 

Washington  
West  Virginia... 
Wisconsin  
Wyoming. 

26.35 
121.10 
2.40 

79.42 
18.50 
83.07 

2,054.00 

Total. 

64,898.43 

10,499.79 

116,058.12 

44,154.73 

1,593.88 

2,348.43 

17,738.16 

257,291.54 

Percent  

25.22 

4.08 

45.11 

17.16 

0.62 

0.91 

6.90 

100.00 

State  roads  only. 


194 


MOTOR-CAR    REGISTRATIONS   AND    GROSS 
MOTOR-VEHICLE  REVENUES,    1913-1915 

Circular  59,   United  States  Department  of  Agriculture.     Prepared  by  the 

Division  of  Road  Economics,  Office^  of  Public  Roads  and  Rural 

Engineering 


MOTOK-CAR  REGISTRATIONS1 

TOTAL   GROSS   REVENUES 

1013 

1914 

1915 

1913 

1914 

1915 

Alabama  

25,300 

3,613 
3,583 
'100,000 
13,000 

23,200 
2,440 

4,000 
43,000 
220,000 

2,113 
94,656 
45,000 

70,299 
34,550 

7,210 
210,000 
11,022 
14,217 
62,660 

54,366 
46,000 
23,850 
38,140 
5,916 

13,411 
1,091 
8,237 
51,360 
1,898 

134,495 
10,000 
15,187 
86,156 
a3,000 

13,975 
80,178 
10,295 
10,000 
14,457 

8,672 
5,040 
5,642 
123,504 
17,756 

27,786 
3,050 

4,833 
43,368 
20,915 

3,346 
131,140 
66,500 

106,087 
49,374 

11,766 
212,000 
15,700 
20,213 
77,246 

76,389 
67,862 
5,694 
54,468 
10,200 

16,385 
1,487 
9,571 
62,961 
3,090 

168,223 
14,677 
17,347 
122,504 
13,500 

16,447 
112,854 
12,331 
14,000 
20,929 

11,634 

7,753 
8,021 
163,797 
28,894 

41,121 
5,052 

8,009 
'10,850 
25,000 

7,071 
180,832 
96,915 

145,109 
72,520 

19,500 
11,380 
21,545 
31,047 
102,633 

114,845 
93,269 
9,669 
76,462 
14,540 

59,000 
2,009 
13,449 
81,848 
5,100 

255,242 
21,000 
24,908 
181,332 
25,032 

23,585 
160,137 
16,362 
15,000 
28,724 

$83,000 
27,545 
17,411 
75,000 
60,833 

316,667 
24,735 

13,228 
46,000 
12,000 

35,160 
507,629 
150,345 

787,411 
186,066 

52,000 
210,000 
138,509 
150,000 
764,154 

190,329 
40,000 

$113,202 
34,077 
56,420 
1,338,785 
80,047 

406,623 
35,672 

20,147 
46,736 
104,575 

58,580 
699,725 
432,309 

1,040,136 
268,471 

85,883 
212,000 
192,542 
268,231 
923,961 

(8) 
132,398 
51,146 
235,873 
27,000 

34,325 
4,331 
185,288 
814,536 
19,663 

1,529,852 
89,580 
55,964 
685,457 
13,500 

77,592 
1,185,039 
157,020 
14,000 
125,000 

$180,744 
45,579 
80,551 
2,027,432 
120,801 

536,970 
55,596 

29,396 
260,000 
125,000 

121,259 
924,906 
587,318 

1,533,054 
387,588 

117,117 
75,600 
268,412 
386,565 
1,235,724 

373,833 
2160,540 
76,700 
323,289 
33,120 

2183,000 
7,875 
257,776 
1,062,923 
29,625 

1,991,181 
123,000 
79,245 
984,622 
154,892 

108,881 
1,665,276 
206,440 
15,000 
'180,000 

Arizona  

Arkansas  

California  

Colorado 

Connecticut  
Delaware 

District  of  Col- 
umbia   

Florida  

Georgia  

Idaho 

Illinois  . 

Indiana  

Iowa 

Kansas 

Kentucky  .... 

Louisiana  .  .  . 

Maine 

Maryland  

Massachusetts.  . 
Michigan  

Minnesota  

Mississippi 

Missouri  

173,510 
12,000 

26,000 
3,323 
152,834 
661,446 
15,084 

1,275,727 
60,000 
41,961 
457,538 
3,000 

56,873 
841,062 
129,851 
10,000 
89,170 

Montana  

Nebraska  

Nevada  

New  Hampshire 
New  Jersey  

New  Mexico  
New  York.  .  .  . 

North  Carolina. 
North  Dakota.  .  . 
Ohio  

Oklahoma  
Oregon 

Pennsylvania..  . 
Rhode  Island.  .  . 
South  Carolina2. 
South  Dakota... 

195 


Motor-Car  Registrations — Continued 


MOTOR-CAB  REGISTRATIONS1 

TOTAL  GROSS  REVENUE* 

1913 

1914 

1915 

1913 

1914 

1915 

Tennessee.. 

'10,000 

32,000 
4,000 
5,913 
9,022 

24,178 
5,144 
34,346 
1,584 

619,769 
40,000 
2,253 
8,475 
13,984 

30,253 
6,159 
53,161 

2,428 

«7,618 
740,000 
9,177 
11,499 
21,357 

38,823 
13,279 
79,741 
3,976 

29,000 

16,000 
3,000 
111,460 
83,611 

48,356 
40,000 
190,770 
7,920 

39,538 
20,000 
4,852 
154,267 
120,814 

60,506 
60,648 
293,580 
12,140 

'34,000 
20,000 
260,000 
218,480 
176,875 

238,717 
128,952 
431,977 
19,880 

Texas1. 

Utah  

Vermont  

Virginia  

Washington  
West  Virginia.  .  . 
Wisconsin 

Wyoming  

Total  

1,258,062 

1,711,339 

2,445,664 

8,192,253 

12,381,951 

18,245,711 

1  Does  not  include  motor  cycles  nor  dealers'  and  manufacturers'  licenses. 

2  Estimated. 

3  Registration  law  declared  unconstitutional. 

4  State  registrations  only. 

6  Total  cars  registered  under  perennial  system. 
8  Registrations  1915  only. 

'American  Highway  Association  received  report  that  there  were  138,866 
automobiles  licensed  on  April  1,  1916. 


PRODUCTION  OF  VITRIFIED  PAVING  BRICK 
IN  THE  UNITED  STATES 

(From  "Mineral  Resources  of  the  United  States, 


TEAR 

QUANTITY 

VALUE 

AVERAGE  PRICE  PER 
THOUSAND 

thousands 

1895 

381,591 

$3,130,472 

$8.20 

1896 

320,407 

2,794,585 

8.72 

1897 

435,851 

3,582,037 

8.22 

1898 

474,419 

4,016,822 

8.47 

1899 

580,751 

4,750,424 

8.18 

1900 

546,679 

4,764,124 

8.71 

1901 

605,077 

5,484,134 

9.06 

1902 

617,192 

5,744,530 

9.31 

1903 

654,499 

6,453,849 

9.86 

1904 

735,489 

7,557,425 

10.28 

1905 

665,879 

6,703,710 

10.07 

1906 

751,974 

7,857,768 

10.45 

1907 

876,245 

9,654,282 

11.02 

1908 

978,122 

10,657,475 

10.90 

1909 

1,023,654 

11,269,586 

11.01 

1910 

968,000 

11,004,666 

11.37 

1911 

948,758 

11,115,742 

11.72 

1912 

911,869 

10,921,575 

11.98 

1913 

958,680 

12,138,221 

12.66 

1914 

931,324 

12,500,866 

13.42 

1915 

953,335 

12,230,899 

12.83 

196 


OUTPUT  OF  VITRIFIED   BRICK  IN  1914  AND 
1915  BY  STATES 

(From  "Mineral  Resources  of  the  United  States, 


1914 

1915 

Quantity 

Value 

Aver- 
age 
price 

- 
sand 

Quantity 

Value 

Aver- 
age 
price 

thou- 
sand 

Alabama  
Arkansas  
California  
Colorado  
Connecticut 
and  Rhode 
Island  

thousands 

18,679 

* 

1,800 

* 

* 

$248,525 
* 

39,705 

* 

$13.31 
12.14 
22.06 
11.52 

16  03 

thousands 

29,018 
* 

3,182 

* 

* 

$374,387 
* 

66,784 
* 

* 

$12.90 
12.00 
20.99 
11.59 

12  66 

Florida  
Georgia  

* 
16,470 

* 
234,855 

12.00 
14.26 

17,193 

166,086 

9.66 

Illinois  

157,176 

2,086,344 

13.27 

142,689 

1,796,350 

12.59 

Indiana  

42,937 

576,892 

13.44 

35,237 

466,873 

13.25 

Iowa  

14,997 

211,905 

14.13 

20,573 

300,785 

14.62 

Kansas  

50,707 

594,229 

11.72 

47,511 

608,599 

12.81 

Kentucky 

* 

* 

12  74 

* 

# 

10  85 

Michigan 

7,733 

120,562 

15  59 

4,420 

62,238 

14  08 

Minnesota  
Missouri 

* 
26,217 

424,170 

16.12 
16  18 

* 
* 

* 

* 

14.18 
14  62 

Montana  
Nebraska  .  . 

* 

* 
* 

22.50 
11  14 

* 
561 

# 
8,323 

22.01 
14  84 

New  Jersey.  .  .  . 
New  Mexico  
New  York  
Ohio  
Oklahoma  
Pennsylvania.  . 
Tennessee  
Texas 

* 
* 

31,240 
293,381 
9,912 

151,200 

* 

1,684 

* 
* 

515,672 
3,682,230 
127,792 

2,052,676 

* 

23,599 

15.00 
10.40 
16.51 
12.55 
12.89 
13.58 
15.26 
14  01 

* 
24,154 
333,288 
16,537 

124,354 

* 

* 

* 

384,458 
4,017,758 
198,387 

1,638,518 

* 

# 

12.00 
15.92 
12.05 
12.00 
13.18 
14.47 
15  45 

Virginia  
Washington.  .  .  . 
West  Virginia.  . 
Other  Statesf  .  . 

* 
* 

67,750 
39,441 

* 
* 

899,215 
662,495 

10.00 
18.99 
13.27 
16.80 

14,861 
69,474 
59,844 

265,691 
841,067 
853,107 

17.88 
12.11 
14.26 

Total  

931,324 

$12,500,866 

$13.42 

953,335} 

$12,230,899* 

$12.83 

*  Included  in  "Other  States." 

f  Includes  all  products  made  by  less  than  three  producers  in  one  State. 

J  In  the  total  quantity  and  total  value  of  vitrified  brick  are  included, 
respectively,  824,359,000  vitrified  brick  sold  for  paving,  valued  at  $11,114,- 
427,  and  128,976,000  vitrified  brick  sold  for  other  uses,  valued  at  $1,116,472. 


BROKEN  STONE  FOR  ROAD  BUILDING  PRO 
DUCED  IN  THE  UNITED  STATES  IN 
1914  AND  1915 


(From 


'Stone  in  1915,"  G.  F.  Loughlin,  "Mineral  Resources  of 
the  United  States'1 


STATE  OR  TERRITORY 

1 

J14 

1 

915 

Quantity 

Value 

Quantity 

Value 

Alabama.               

Short  tons 

74,914 

$75  528 

Short  tons 
49  972 

$42  116 

Arizona.            

2,600 

4,000 

Arkansas  

199,417 

140,442 

113,606 

75044 

California 

1  707  230 

982  321 

1  567  505 

902  462 

Colorado 

6052 

10  100 

5  842 

7  178 

Connecticut.  . 

360,443 

216  064 

728  014 

330  174 

Delaware          

53,430 

33  501 

21  742 

21  707 

Florida       

159,524 

84,911 

102  517 

56  381 

Georgia  

57,553 

37,088 

90244 

54  696 

Hawaii  

41,832 

37,049 

34,413 

36366 

Idaho 

Illinois        ..        

1,838,599 

893889 

1  625  250 

747  718 

Indiana       

2,089,103 

1,065  360 

1  792  261 

910  462 

Iowa      

19,308 

17,438 

32437 

28  397 

Kansas  

27,248 

20,135 

20,046 

15  591 

Kentucky  

545,878 

323,075 

609,995 

379,234 

Louisiana 

830 

664 

Maine 

5,950 

4  650 

1  747 

1  409 

Maryland 

404,523 

349  833 

334  153 

274  644 

Massachusetts     

649,144 

594  666 

738  015 

599  555 

Michigan     

53Q,823 

267,702 

510,524 

224  734 

Minnesota  

46,944 

36,172 

59,733 

57,286 

Missouri  

466,143 

363,302 

553,049 

383,022 

Montana 

4,590 

1  271 

23  875 

5  186 

Nebraska  

32,137 

27,300 

New  Hampshire    .    ... 

20,936 

13,745 

14845 

12  416 

New  Jersey        

827,705 

674,202 

1,059  749 

822  214 

New  Mexico  

547 

407 

New  York  

2,267,264 

1,408,490 

2,900,165 

1,623,570 

North  Carolina  . 

65700 

65  128 

69  238 

73  404 

Ohio 

3,453,360 

1,748  075 

3  088  599 

1,567  676 

Oklahoma. 

15,802 

7,441 

46430 

29  764 

Oregon..        

218,379 

157,267 

290,648 

202,580 

Pennsylvania  
Rhode  Island  

1,640,049 
61,373 

1,110,039 
72,255 

1,844,626 
91,872 

1,218,446 
110,167 

South  Carolina  
South  Dakota 

28,425 
14,120 

27,684 
11  300 

27,111 
11  292 

26,566 

8487 

Tennessee.. 

345,765 

264  288 

441  298 

369  296 

Texas 

196,051 

119,218 

269,151 

164,865 

Utah  

16,000 

19,200 

6,500 

3,750 

Vermont  
Virginia  

17,978 
1,931,852 

13,563 
1,185,271 

14,929 

2,193,898 

13,269 
1,538,149 

Washington. 

162,777 

87  259 

213  039 

111  461 

West  Virginia 

197,245 

113  525 

196,068 

129,106 

Wisconsin  

1,000,667 

635,618 

914,295 

555,927 

Wyoming.  . 

21,786,833 

13,329,365 

22,710,070 

13,735,546 

198 


GRAVEL  AND  PAVING   SAND  PRODUCED  IN 
THE  UNITED  STATES  IN  1914  AND  1915 

R.  W.  Stone  in  "Mineral  Resources  of  the  United  States,  1915" 


STATE 

PAVING  SAND 

ORAVEL, 

1914 

1915 

1914 

1915 

Quantity 
(short 
tons) 

Value 

Quantity 
(short 
tons) 

Value 

Quantity 

(short 
tons) 

Value 

Quantity 
(short 
tons) 

Value 

Alabama  
Arizona...  . 

5,849 

$4,538 

* 

* 

527,891 

$138,693 

547,656 

* 

831,668 
2,974,090 

* 
16,518 

22,848 

* 

* 
4,424,527 
2,482,922 
1,554,199 

448,897 
* 
854,180 
270,906 
2,457,094 
935,252 
991,119 
1,656,745 
7,422 
118,970 
17,491 

583,200 
2,112,557 

* 

2,828,887 
77,241 

* 

2,816,132 

368,797 
1,814,902 

239,649 
540,653 
1,494.421 
251,216 

* 

519,850 
478,707 
114,273 
1,567,840 

1,551,719 

$116,672 

314,003 
709,602 

* 
* 

4,495 
15,071 

* 
* 

885,548 
591,592 
313,327 

162,524 
* 
284,410 
169,772 
671,970 
175,084 
153,627 
226,716 
5,500 
27,389 
1,775 

77,760 
447,388 

989,801 
23,652 

* 

922,379 

118,960 
433,223 

* 

* 
36,826 
203,867 
393,121 
29,772 
* 

126,801 
129,016 
43.016 
349,941 

443,791 

Arkansas  
California  
Colorado 

106,578 

26,714 

673,924 
3,258,718 
7,610 

278,876 
595,449 
3,310 

173,985 

$42,841 

* 

Connecticut..  . 
Florida  
Georgia  
Hawaii  

* 
29,000 
5,610 

* 
7,000 
1,400 

* 

* 

98,435 
12,244 

10,637 
7,875 

Idaho 

* 
4,955,219 
4,184,093 
1,087,967 
160,283 
815,796 
738,510 

760,204 
177,642 
2,140,359 
637,900 
1.500,291 
1,321,839 
13,310 
88,026 

670,000 

2,204,880 

* 

2,149,310 
311,059 
10,875 
2,417,805 
505,737 
611,821 
1,766,651 

29,927 
196,909 
445,504 
1,183,646 
184,763 
822 
294,398 
457,137 
455,804 
1,294,893 
718,441 

142,215 

* 

793,422 
602,533 
205,820 
19,512 
208,770 
190,717 

268,338 
50,795 
530,338 
236,704 
354,855 
257,827 
11,970 
16,435 

112,500 
672,433 

891,762 
42,438 
5,725 
654,833 
225,559 
137,221 

387,845 

* 

4,995 
25,603 
183,296 
433,399 
45,162 
390 
87,379 
162,183 
125,618 
343,230 
48,245 

26,205 

Illinois  

121,812 
158,443 
201,900 
137,582 

21,653 

* 

39,851 
55,290 
64,340 
37,206 
14,272 

291,436 
240,053 
293,948 

244,103 

* 

73,645 
66,894 
97,008 

70,311 

* 

Indiana  
Iowa  
Kansas  
Kentucky  
Louisiana  
Maine 

Maryland  
Massachusetts.. 
Michigan  
Minnesota 

327,750 
78,380 
320,322 
36,458 

76,212 
33,161 

74,806 
15,666 

163,304 
47,239 
131,466 

71,517 
25,444 
14,021 

Mississippi  

Missouri  
Montana  
Nebraska  
Nevada  

30,327 
5,259 

6,485 

* 

610 

New      Hamp- 
shire. 

New  Jersey  
New  Mexico 

110,260 

39,902 

160,256 
51,363 

53,599 

* 

21,240 

New  York  
North  Carolina 
North  Dakota. 
Ohio  
Oklahoma 

82,725 

34,148 

407,025 

134,370 

501,359 

194,026 

Oregon  

3,368 
625,171 

2,607 
235,326 

15,218 
291,599 

14,174 

106,828 

Pennsylvania.  .  . 
Rhode  Island... 
South  Carolina. 
South  Dakota.  . 
Tennessee  
Texas 

* 

6,489 
46,460 
44,445 

* 
2,484 
14,315 
11,300 

• 
13,815 
11,904 

* 

* 
3,552 

2,950 

* 

Utah  
Vermont  . 

Virginia  

* 

363,745 
44,617 
.    222,298 

* 

86,796 
17,819 
71,560 

83,827 
69,598 
206,094 

27,628 
27,230 
67,340 

Washington  
West  Virginia... 
Wisconsin  
Wyoming 

Concealed 
totals  

36,645 

13,761 

391,150 

97,138 

3,580,171 

1,121,999 

3,381,717 

1,077,346 

39,212,858 

9,398,897 

37,972,548 

9.598,391 

Included  in  "Concealed  totals.' 


199 


THE  REASONS  FOR  IMPROVING  ROADS 

Good  roads  are  desirable  for  three  distinct  reasons,  which  may 
be  called  social,  business  and  pleasure  reasons. 

Social  Benefits  from  Good  Roads. — The  social  reasons  for  road 
improvements  appeal  to  persons  living  in  the  country.  The 
women  who  dwell  in  the  country  districts  know  better  than  any 
others  what  bad  roads  mean  to  themselves  and  their  sisters  on 
other  f  atms,  and  how  utterly  drab  and  hopeless  is  life  in  the  coun- 
try with  inadequate  means  of  communication  between  themselves 
and  almost  their  next-door  neighbors.  The  country  parson  can 
tell  what  a  handicap  bad  roads  are  in  his  work.  Preaching  two 
sermons  on  Sunday  is  but  a  part  of  his  labors.  He  must  visit 
his  parishioners  if  he  is  to  be  the  guide,  counselor  and  friend  he 
aspires  to  be.  He  knows  by  hard  experience  the  difficulty  of 
riding  or  walking  over  muddy  roads  and  through  oceans  of  slush 
to  those  longing  for  his  comforting  presence  in  time  of  sickness 
and  death,  and  how  hard  it  is  to  convey  to  those  who  are  ill  the 
things  necessary  for  their  recovery.  The  country  doctor  can 
likewise  bear  witness  to  the  restraint  and  even  suffering  caused 
by  bad  roads.  Taking  men  as  they  are  in  the  large,  the  wonder 
is  that  there  are  any  who  would  choose  his  profession,  the  most 
devoted  and  consecrated  of  all  that  serve  humanity.  He  comes 
when  he  is  called  and  where.  His  charity  is  unmeasurable,  his 
rewards  are  insignificant.  Time  with  him  and  with  the  patient 
waiting  his  aid  is  often  the  deciding  factor  between  life  and  death; 
he  knows  full  well  the  death  rate  due  to  isolation  by  poor 
highways. 

We  cannot  state  in  percentages  the  increase  in  the  satisfaction 
of  people  with  country  life  which  follows  the  certainty  a  doctor 
can  be  obtained  when  he  is  needed.  It  is  not  yet  possible  to 
state  in  numerals  how  much  better  a  man  is  for  attending  church 
regularly  or  how  much  better  a  farmer's  wife  is  for  driving  over  a 
good  road  whenever  she  wishes  to  call  on  her  neighbors.  But 
there  is  one  thing  to  which  everybody  will  agree;  the  schools  of 
our  rural  territory  are  one  of  the  great  defenses  of  our  national 
prosperity,  and  the  education  of  our  children  is  one  of  our  best 
safeguards  for  the  wise  government  of  our  republic.  And  so 
everyone  will  admit  the  importance  of  these  figures:  In  eight 
typical  rural  counties  studied  by  the  U.  S.  Office  of  Public  Roads 
during  a  period  of  five  years,  the  average  school  attendance  in- 
creased from  66  out  of  every  100  pupils  enrolled  before  the  roads 
were  improved,  to  76  out  of  every  100  after  the  improvements. 

200 


REASONS  FOR  IMPROVING  ROADS 


201 


Ten  per  cent  more  children  were  helped,  therefore,  to  become 
better  citizens  by  an  increase  in  taxation  for  roads  amounting  to 
only  9  per  cent  of  the  total  tax  for  all  purposes. 

Business  Benefits  from  Good  Roads. — The  business  advantages 
of  road  improvements  to  the  owner  of  a  farm  can  be  stated  even 
more  definitely,  for  they  can  be  measured  in  dollars  and  cents. 
In  the  investigation  by  the  U.  S.  Office  of  Public  Roads,  just 
mentioned,  the  observations  were  carried  out  in  New  York, 
Virginia,  Alabama,  Florida  and  Mississippi,  in  districts  which 
represent  typical  dairying,  farming,  mining  and  lumbering  con- 
ditions, before  and  after  the  construction  of  roads.  The  amount 
of  road  improvements  done  in  each  of  them,  which  produced  the 
improved  conditions  which  will  be  stated,  were  as  follows: 


COUNTY 

MILES  0 

P   ROADS 

Total 

Improved 

Franklin,  N.  Y.. 

1,370 

369 

Spotsylvania,  Va.        

400 

83 

Dinwiddie,  Va  

524 

101 

Lee,  Va  
Wise  Va 

450 
300 

105 
146 

Dallas,  Ala  
Manatee,  Fla  

1,000 
575 

218 
64 

Lauderdale,  Miss 

800 

147 

The  investigations  by  the  government's  experts  were  not  hasty 
observations  from  a  buggy  or  automobile;  they  were  painstaking 
searches  through  real-estate  transfers,  public  records,  railway 
reports,  school  reports  and  like  sources  of  information,  studied  on 
the  spot  until  their  accuracy  was  fully  established.  They  were 
made  from  year  to  year,  moreover,  to  make  sure  that  the  local 
conditions  were  fully  understood  and  the  annual  effect  of  a  road 
improvement  was  ascertained  beyond  question. 

Real  estate  transfers  showed  that  the  percentage  of  increase 
in  the  value  of  rural  property  along  these  improved  roads  in  about 
five  years  was  as  follows:  Franklin,  9  to  114;  Spotsylvania,  63  to 
80;  Dinwiddie,  68  to  194;  Lee,  70  to  80;  Wise,  25  to  100;  Dallas, 
50  to  100;  Manatee,  50  to  100;  Lauderdale,  25  to  50.  The 
transfers  on  which  these  figures  are  based  are  mostly  for  prop- 
erty within  a  mile  of  the  improved  roads. 

In  each  county  the  extent  of  the  districts  sending  vehicles  to 
the  improved  road  was  carefully  determined  in  much  the  same  way 
that  the  drainage  area  of  a  stream  is  ascertained.  The  products 
of  these  districts  and  the  proportion  of  them  hauled  over  the 
roads  were  then  ascertained.  The  railway  shipments  from  and 


202  AMERICAN   HIGHWAY  ASSOCIATION 

into  the  districts  were  investigated.  In  case  of  doubt  the  actual 
travel  on  the  roads  was  ascertained  by  counts  of  the  vehicles  and 
their  loads.  The  average  length  of  the  haul  on  the  roads  was 
found  out.  From  all  these  statistics,  given  in  detail  in  the  report, 
it  is  shown  that  the  cost  of  hauling  one  ton  one  mile  on  the  roads 
of  these  counties  was  decreased  from  an  average  of  33.5  cents 
before  highway  improvements  were  made  to  15.7  cents  after- 
ward. This  saving  of  17.8  cents  per  ton  per  mile  amounts  to 
$627,409  in  all.  To  accomplish  it  the  additional  taxes  amounted 
to  only  6.3  cents  per  ton  per  mile,  leaving  a  net  saving  of  11.6 
cents  per  ton  per  mile. 

Roads  as  Sources  of  Enjoyment. — It  is  unfair  to  object  to  includ- 
ing the  pleasure  obtained  by  riding  comfortably  through  the 
country  as  one  of  the  returns  we  receive  from  our  road  taxes. 
It  is  just  as  proper  to  include  that  kind  of  pleasure  as  a  justifiable 
object  of  expenditure  as  the  investments  for  liquors,  tobacco,  the 
theatre  and  confectionery.  E.  W.  James,  one  of  the  road  experts 
of  the  United  States  government,  recently  made  the  following 
statement  on  the  subject: 

The  people  of  the  United  States  spent  in  1915  $2,500,000,000  for  spiritu- 
ous and  malt  liquors  $800,000,000  for  tobacco,  $450  000,000  for  the  "mov- 
ies," $300,000,000  for  candy,  $200,000,000  for  soda  water  and  $50,000,000 
for  chewing  gum.  The  total  for  these  pleasures  is  $4,300,000,000.  So  I 
think  it  conservative  to  say  that  the  average  man  is  willing  to  pay  some- 
thing for  pleasure.  There  can  be  no  question  about  the  pleasure  derived 
from  riding  on  good  roads,  and  that  a  part  of  the  money  invested  in  such 
roads  can  be  logically  justified  on  the  score  of  this  pleasure.  After  all, 
the  total  annual  expenditures  on  roads  in  the  United  States  is  only  equal 
to  our  purchase  of  candy  and  merely  one-eighth  of  the  money  spent  on 
liquor. 

The  Townsman's  Interest  in  City  Roads. — When  the  average 
townsman  dresses  in  the  morning,  a  large  part  of  the  clothes  he 
puts  on  are  made  of  cotton,  which  has  to  be  teamed  over  a  good 
many  miles  from  the  plantations  to  the  shipping  points.  If  he 
has  fruit,  cereal,  eggs  and  toast  for  breakfast,  let  us  say,  about 
everything  he  eats  has  been  hauled  over  several  miles  of  roads, 
either  to  be  shipped  to  him  or  to  the  mills  where  it  is  prepared  for 
shipment.  A  large  part  of  the  furniture  in  his  home  and  at  his 
office  has  been  made  from  hardwood  hauled  over  the  roads. 
These  and  other  things  which  anybody  can  list  for  himself  must 
all  vary  in  price  to  the  townsman  with  the  cost  of  hauling  them 
from  the  farms  and  forests  to  the  mills  or  railroad  stations.  Just 
what  this  fact  means  has  been  stated  by  J.  E.  Pennybacker,  the 
highway  economist  of  the  United  States  Office  of  Public  Roads, 
as  follows: 


REASONS   FOR  IMPROVING  ROADS  203 

The  public  roads  throughout  the  country,  which  constitute  the  primary 
means  of  transportation  for  all  agricultural  products,  for  many  millions 
of  tons  of  forest,  mine  and  manufactured  products,  and  which  for  a  large 
percentage  of  farmers  are  the  only  avenues  of  transportation  leading  from 
the  point  of  production  to  the  point  of  consumption  or  rail  shipment, 
have  been  improved  to  only  a  slight  extent.  By  reason  of  this  fact,  the 
prevailing  cost  of  hauling  over  these  roads  is  about  23  cents  per  ton  per 
mile.  More  than  350,000,000  tons  are  hauled  over  these  roads  each  year, 
and  the  average  haul  is  about  8  miles,  from  which  it  can  readily  be  seen 
that  our  annual  bill  for  hauling  over  the  public  roads  is  nearly  $650,000,000. 
The  cost  per  ton-mile  for  hauling  on  hard  surfaced  roads  should  not  exceed 
13  cents.  It  is  therefore  evident  that  if  our  roads  were  adequately  im- 
proved a  large  annual  saving  in  the  cost  of  hauling  would  result. 


The  difference  between  23  and  13  cents  is  10  cents,  which  is 
the  ton-mile  tax  of  poor  roa,ds  which  the  city  people  pay,  for  most 
of  the  hauling  is  toward  markets  or  shipping  points  and  the  cost 
of  this  hauling  is  part  of  the  total  expense  of  products  of  the  land 
to  the  consumer.  The  total  is  about  $280,000,000,  which  the 
45,000,000  people  living  in  the  cities  and  towns  of  the  United 
States  pay  annually  on  account  of  poor  roads.  This  averages 
over  $6  a  year  per  person. 

Poor  roads  put  a  much  more  serious  drain  on  the  townsman's 
pocket-book,  however.  His  food  is  costing  him  more  every  year, 
and  he  therefore  has  a  very  close,  personal  interest  in  having  the 
agricultural  lands  farmed  in  such  a  way  that  they  yield  their 
largest  returns  at  the  lowest  working  cost.  This  means  more 
than  producing  milk  and  vegetables  at  a  low  cost;  it  also  includes 
raising  at  low  expense  the  wheat  and  corn  from  which  his  flour 
and  meal  are  made,  producing  fowls  and  hogs  economically,  and 
reducing  the  cost  of  growing  cotton.  How  many  intelligent 
young  men,  able  to  earn  a  good  living  in  a  city,  will  live  in  the 
country  if  they  have  to  travel  through  miles  of  mud  or  dust,  at 
decided  physical  discomfort,  in  order  to  market  their  products, 
meet  their  friends  or  buy  their  supplies?  How  many  young 
women  will  be  willing  to  live  in  the  country  where  bad  roads 
isolate  them,  with  only  the  sparrows  for  companions,  with  the 
doctor  almost  inaccessible,  the  schools  difficult  for  the  children 
to  reach,  and  church-going  a  real  labor?  Yet  if  the  townsman  is 
to  have  the  things  he  eats  grown  for  him  efficiently  and  economi- 
cally he  must  take  his  part  in  making  country  life  agreeable  and 
profitable  to  these  intelligent  young  people.  It  means  a  saving 
of  dollars  and  cents  to  him. 

Our  American  Roads. — The  length  of  the  rural  roads  in  the 
United  States  at  the  close  of  1915  is  given  in  the  table  on  page 
192.  This  table  shows  that  only  11.3  per  cent  of  the  total  mile- 
age at  that  time  had  been  surfaced,  and  that  only  2  per  cent  had 


204  AMERICAN  HIGHWAY  ASSOCIATION 

been  built  by  the  state  highway  departments  or  with  more  or  less 
financial  or  engineering  assistance  from  the  states. 

It  has  been  estimated  that  about  80  per  cent  of  the  total  travel 
on  these  roads  is  done  on  about  15  per  cent  of  their  total  length. 
The  percentages  vary  in  different  states.  The  Iowa  Highway 
Commission  found  that  from  10  to  15  per  cent  of  the  roads  of  each 
county  are  main  traveled  routes,  which  it  is  proper  to  construct 
and  maintain,  under  the  Iowa  highway  laws,  at  the  expense  of 
the  county  as  a  unit.  The  remaining  roads  are  of  less  general 
use  and  are  constructed  and  maintained  by  the  townships  through 
which  they  pass. 

This  division  of  our  highways  into  main  routes  and  local  roads 
is  of  fundamental  importance  in  road  administration.  Public 
money  must  be  used  so  as  to  yield  the  greatest  good  to  the  great- 
est number  of  people.  But  it  is  human  nature  for  a  man  living 
a  mile  or  more  from  a  main  road  to  complain  that  he  is  unfairly 
treated  if  he  must  travel  over  a  dirt  road  part  of  the  way  to  town 
while  a  neighbor  has  a  good,  hard-surfaced  road  running  by  his 
place.  As  a  matter  of  fact,  although  the  hard  road  does  not 
reach  his  farm  it  does  help  him  materially,  as  Prof.  B.  K.  Cogh- 
lan,  of  the  Texas  Agricultural  and  Mechanical  College  has 
shown  by  a  recent  investigation.  He  reports: 

Where  a  farmer  lives  at  a  considerable  distance  from  the  improved 
road  he  will  still  derive  some  benefit.  In  one  county,  where  the  gravel 
roads  extend  only  about  8  miles  from  town,  the  farmers  living  several 
miles  beyond  haul  wood  during  the  dry  spells  and  pile  it  at  the  end  of  the 
gravel  road;  then  when  bad  weather  comes  and  it  is  impossible  to  work  in 
the  fields  they  haul  this  wood  to  town.  In  another  case  two  teams  are 
used  until  the  improved  road  is  reached,  when  one  team  is  unhitched  and 
left  with  a  friend,  and  the  man  proceeds  to  town  with  the  other.  In  a 
third  instance,  where  it  formerly  took  two  days  to  haul  a  load  to  market, 
since  a  good  road  has  been  built  for  about  one-half  of  the  distance,  two 
wagons,  with  two  teams  each,  haul  one  day  until  the  good  road  is  reached 
when  all  the  load  is  put  on  one  wagon,  which  proceeds  to  town  with  one 
team,  the  other  three  teams  returning  home. 

Our  main  roads  which  carry  four-fifths  of  the  traffic  present 
problems  which  are  often  quite  different  from  those  of  the  local 
roads.  Highways  must  be  built  to  carry  the  traffic  over  them  at 
the  lowest  possible  cost  for  both  construction  and  maintenance. 
Where  the  traffic  is  light,  as  on  local  roads  and  some  main  roads, 
comparatively  inexpensive  types  of  construction  can  be  main- 
tained at  small  expense  and  are  therefore  better  than  more  ex- 
pensive types  because  more  miles  of  them  can  be  provided  for 
the  same  total  cost  than  is  the  case  with  expensive  types  of  con- 
struction. As  a  rule,  however,  we  are  trying  to  get  too  much 
work  from  inexpensive  roads  and  at  the  same  time  we  are  neglect- 


REASONS  FOR  IMPROVING  ROADS  205 

ing  to  maintain  them  in  a  condition  for  giving  the  most  service. 
For  many  years  to  come,  a  large  part  of  our  roads  will  be  earth, 
top-soil,  sand-clay  and  gravel.  That  is  no  reason,  however,  for 
their  being  mud  holes  in  wet  weather  or  sources  of  blinding  dust 
in  dry  weather.  Well  graded,  drained  and  maintained  roads  of 
these  types  are  pleasant  to  ride  over  and  inexpensive  to  maintain, 
unless  they  are  called  upon  to  carry  more  travel  than  they  are 
capable  of  supporting.  Then  they  fail  just  as  a  beam  fails  when 
it  is  overloaded.  The  beam  is  ajl  right  for  a  given  loading,  but 
all  wrong  for  a  greater  one.  A  road  may  be  all  right  for  a  certain 
travel  but  all  wrong  for  a  greater  travel;  the  failure  to  recognize 
this  is  responsible  for  a  large  part  of  the  waste  of  road  taxes 
today. 

Different  Classes  of  Road  Improvements. — The  improvement  of 
roads  comprises  a  number  of  classes  of  work.  People  who  speak 
of  road  improvements  in  Missouri  probably  refer  to  grading  and 
draining,  while  road  improvements  in  Massachusetts  usually 
signify  the  construction  of  a  hard  surface  on  a  road  already 
graded  and  drained.  Such  use  of  the  word  "improvements'7 
indicates  how  varied  are  the  really  pressing  highway  needs  of 
different  parts  of  the  country  and  the  importance  of  studying  the 
local  resources  and  transportation  requirements  of  a  district  be- 
fore planning  the  improvement  of  its  roads. 

The  first  thing  to  be  considered  in  planning  good  roads  is  the 
amount  of  money  which  it  is  wise  for  a  community  to  spend  for 
them.  Most  estimates  of  this  nature  are  based  on  the  existing 
annual  tax  receipts  available  for  the  purpose.  This  is  not  the  best 
basis  for  a  sound  judgment.  A  family  of  three  persons  can  make 
an  income  of  $1800  go  farther  than  a  family  of  six  persons  can.  It 
is  the  same  with  rdads.  To  find  out  roughly  how  much  money 
can  be  devoted  to  road  work  it  is  best  to  divide  the  assessed  valu- 
ation of  the  district  by  the  miles  o£  roads  in  it.  This  gives  the 
valuation,  or  taxable  wealth,  of  the  district  per  mile  of  road. 
For  instance,  Lake  County,  Mich.,  has  a  valuation  of  only  $5420 
per  mile,  showing  that  not  even  the  entire  wealth  of  the  county 
is  sufficient  to  improve  all  its  roads.  Wayne  County,  Mich.,  on 
the  other  hand,  has  a  valuation  of  $514,931  per  mile,  indicating 
its  financial  ability  to  carry  out  any  kind  of  road  improvements 
in  reason.  In  a  rich  agricultural  district  like  Calhoun  County, 
Mich.,  the  valuation  is  $52,294  per  mile,  indicating  that  it  is 
financially  able  to  construct  whatever  kind  of  main  roads  may 
be  best  suited  for  the  travel  on  them.  We  look  with  pity  on  the 
young  saleswoman  who  spends  all  her  money  on  clothes  she  does 
not  need,  and  yet  we  complain  when  a  county  with  a  very  low 
valuation  per  road-mile  is  not  intersected  with  roads  as  smooth 


206  AMERICAN   HIGHWAY  ASSOCIATION 

as  the  top  of  a  billiard  table.  This  shows  that  we  have  our  fool- 
ish ideas,  like  the  flighty  saleswoman. 

There  is  a  measure  of  the  need  for  roads,  just  as  there  is  a 
measure  of  the  financial  resources  for  roadbuilding.  This  meas- 
ure is  the  travel  the  road  is  carrying  now  and  the  probable  in- 
crease in  the  travel  during  the  next  five  to  ten  years.  The  im- 
provement of  a  country  road  results  in  the  slow  development  of 
property  along  it,  so  that  there  is  a  slow  annual  increase  in 
what  is  called  the  residential  travel.  If  the  road  is  on  a  through 
route  between  important  cities  some  distance  apart,  there  may 
or  may  not  be  a  material  increase  in  the  foreign  travel,  by  which 
is  meant  the  travel  between  these  cities.  This  can  only  be  de- 
termined by  a  study  of  local  conditions.  The  residential  travel 
can  be  actually  counted,  however,  and  this  ought  to  be  done. 
The  state  highway  department  or  the  United  States  Office  of 
Public  Roads  and  Rural  Engineering  at  Washington  will  furnish 
instructions  for  the  work,  which  can  be  done  by  school  children 
under  the  direction  of  their  teachers.  This  is  a  kind  of  child 
labor  which  no  reformer  will  weep  over  and  the  efficiency  expert 
will  approve. 

The  travel  over  a  road  wears  it  out  in  different  ways,  according 
to  the  number  and  character  of  the  vehicles,  the  relative  propor- 
tion of  horse-drawn  vehicles  and  automobiles,  the  climatic  con- 
ditions and  the  construction  of  the  road.  For  the  same  travel, 
a  road  adopted  for  a  moist  section  with  cold  winters  is  needlessly 
expensive  for  a  dry  section  with  little  frost.  Some  types  of  roads 
wear  out  quickly  but  are  easily  maintained,  other  types  with- 
stand travel  well  but  when  they  need  repairs  the  work  is  expen- 
sive. All  these  things  must  be  considered  in  determining  the 
annual  cost  of  a  road,  which  is  done  in  the  following  way. 

The  first  element  of  this  cost  is  the  first  cost  of  construction  per 
mile  of  road,  including  all  engineering  expenses.  Knowing  the 
travel  over  the  road,  an  expert  can  estimate  the  number  of  years 
such  a  road  will  serve  its  purpose,  if  properly  maintained,  before 
reconstruction  is  necessary.  This  cost  divided  by  the  number  of 
years  of  service  gives  the  annual  first  cost.  To  this  must  be  added 
the  annual  interest  on  the  first  cost  per  mile.  If  the  construction 
costs  are  met  by  the  proceeds  of  a  bond  issue,  the  interest  and 
sinking  fund  charges  on  the  bonds  take  the  place  of  the  annual 
first  cost  and  interest  just  mentioned.  The  annual  cost  per  mile 
of  maintaining  the  road  in  serviceable  condition  is  the  last  item 
to  be  estimated.  The  sum  of  all  these  items  is  the  total  annual 
cost  per  mile  of  the  road,  and  this  figure  is  the  most  important 
one  to  the  taxpayers.  But  another  unit  for  measuring  cost, 
which  is  sometimes  very  useful,  is  the  cost  of  the  road  per  vehicle 
mile.  This  is  obtained  by  dividing  the  total  annual  cost  per 


REASONS  FOR  IMPROVING  ROADS  207 

mile  by  the  number  of  vehicles  using  the  road  annually.  The 
type  of  construction  which  gives  the  lowest  cost  per  vehicle  mile 
is  generally  the  best  to  employ. 

While  the  preceding  notes  explain  the  steps  to  be  taken  in 
planning  a  good  road,  they  cannot  supply  the  good  judgment 
necessary  to  take  the  steps  wisely.  We  admire  the  skill  of  a 
slack-rope  gymnast  but  we  are  not  foolish  enough  to  emulate 
him.  The  skill  and  knowledge  needed  to  select  the  right  type  of 
construction  for  a  road  are  greater  than  those  required  by  the 
slack-rope  performer,  and  yet  our  minds  are  so  warped  by  con- 
stant use  of  roads  that  we  are  strongly  inclined  to  think  we  are 
able  to  do  the  work  of  road  engineers.  We  wn^  ^e  losing  money 
in  our  road  planning  until  we  stop  this  foolishness. 


INDEX 


Absorption  of  water  by  earth,  20 
Accidents,  on  roads,  25 
Aggregates  for  concrete,  93 
Alabama,  road  mileage,  192,  193, 194 
Andesite,  76,  87 

properties,  77 
Annuity  bonds,  187 
Appalachian  oil  fields,  110 
Arid  regions,  roads,  46 
Arizona,  funds  for  roads,  193 

motor  cars,  195 

road  mileage,  192,  194 
Arkansas,  funds,  193,  195 

motor  cars,  195 

road  mileage,  192,  194 
Aspha-bric,  176 
Asphalt,  see  Bitumen 

Bermudez,  120 

blocks,  148 

California,  122 

Cuban,  122 

definitions,  117 

Maracaibo,  122 

Mexican,  122 

mixers,  145 

natural,  118 

oil,  118 

Trinidad,  118 
Asphaltenes,  116 
Augite,  321 

Automobile  accidents,  25 
Automobile  registration,  193 


Banking  curves,  230 
Basalt,  75,  87 

properties,  76 
Base,  see  Foundation 
Belts  for  finishing  concrete,  OT  8 
Berm  ditches,  22 
Bermudez  asphalt,  120 
Binders,  bituminous,  124 

clay,  51,  52,  53,  56,  58 

glutrin,  72 

gravel  and  screenings,  71 ,  72 

iron  oxide,  51 

rock  powder,  53 
Biotite,  83 
Bitumen,  definition,  117 

ductility,  126 

fixed  carbon,  116 

float  test,  125 

fluxing  solid,  123 

gilsonite,  122 

grahamite,  123 

hydrocarbons,  116 

inorganic  matter,  116 

insoluble  organic  matter,  116,  121 

manjak,  123 

native  solid,  117 

paraffin,  116 

penetration,  121 

solid,  semi-solid  and  liquid,  117 

solubility  in  carbon  disulphide,  114 

in  carbon  tetrachloride,  122 

in  naphtha,  116 

viscosity,  125 
Bituminous  fillers  for  joints,  173 


Bituminous  roads,  138 

concrete,  144 

macadam,  139 
Blasting,  38 
Blowing  oils,  114,  116 
Bonds,  180 
Box,  57,  60,  69 
Brick,  paving,  157 

cubical,  176 

impregnated  with  asphalt,  176 

production,  196,  197 
Brick  roads,  157 

on  1-inch  concrete  base,  178 
Bridges,  34 

avoided  by  relocation  of  roads,  2 

overflow,  36 

size  of  waterways,  254 
Byerly  process  of  blowing  oils,  114 

Calcite,  84 
Calcium  chloride,  74 
California  asphalt,  122 

banking  curves,  9 

funds  for  roads,  193 

motor  cars,  195 

oil,  110 

regulations  regarding  surveys  and  plans,  12 

road  mileage,  192,  194 
Carbon  disulphide  test  for  bitumens,  114 
Catchbasins,  29 
Cement,  standard  specifications  for  Portland, 

107 
Cementing  value  of  rock  powders,  85 

test,  86 
Chert,  75,  88 
Chlorite,  84 
Clay,  absorption  and  retentivity,  20 

for  sand-clay  roads,  47 

slope  in  cuts  and  fills,  5 
Clearing  right-of-way,  39 
Colorado,  funds  for  roads,  193 

motor  cars,  195 

road  mileage,  192, 194 
Concrete,  cement,  curing,  103 

expansion  and  contraction,  100 

finishing,  102 

mixing,  97, 101 

placing,  98 

proportions,  95 

quantities  of  sand,  cement  and  stone  re- 
quired for  roads  of  different  widths  and 
thicknesses,  96,  97 
Concrete,  bituminous,  144,  155 
Concrete  roads,  90 

surfacing,  154 
Connecticut,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Contracts,  plans  for,  4 
Costs   per   mile   corresponding   to   different 

costs  per  square  yard,  70 
Cross-drains,  27,  91 
Cross-sections  of  roads,  concrete,  92 

influence  on  drainage,  20 

Wisconsin  standards,  6 
Crown  of  roads,  21,  92 
Crushing  gravel,  54 

rock,  66 


209 


210 


INDEX 


Cuban  asphalt,  122 
Culverts,  32 

avoided  by  relocation,  23 

driveway,  26 

headwalls,  33 

size,  29 
Curbs,  162 
Curves,  8,  9 
Cushion  for  brick,  165 
Cut-back  bituminous  products,  133 
Cuts,  38,  42 

Deferred  serial  bonds,  188 
Delaware,  road  mileage,  192,  194 

funds,  193 

motor  cars,  195 
Deval  test,  86 
Diabase,  75,  87 

properties,  77 
Diorite,  75,  87 

properties,  77 
Distillation  test  of  tar,  137 
Distributors  of  oil,  142 
Ditches,  24 

accidents  by  ditching  vehicles,  26 

berm  ditches,  22,  24 

marsh-road,  21 

outlets,  22,  26 

recommendations  of  American  Railway  En- 
gineering Association,  23 

steep  grades,  19,  25 

summits  in,  25 

water  brakes,  25 
Dolomite,  84,  87 

properties,  80 
Dragging,  earth  roads,  43 

embankments  during  construction,  40,  43 

gravel  roads,  56,  57,  63 

road  plane,  40 

sand-clay  roads,  49 
Drainage,  19,  68,  91 

size  of  culverts,  30 
Driveway  culverts,  26 
Dubbs  process  of  refining  petroleum,  113 
Ductility  test  of  bitumens,  126 
Dumping  boards,  70,  141 
Dun's  culvert  formula,  31 
Durax  pavements,  176 

Earth  roads,  32 

oiling,  146 
Embankments,  39,  42 

accidents  on,  25 

building  in  layers,  39,  90 

drainage,  23,  24,  29 

in  flat  country,  22 

in  marshes,  21 

protection  against  scouring,  28,  33 

slopes,  5 
Engineering,  bridge,  35 

importance  in  road  work,  3 

regulations   of   California   commission   re- 
garding surveys  and  plans,  12 

Excavation,  38 
Expansion  joints,  99,  174 

Feather-edge  gravel  and  broken  stone  roads,  57 

Feldspar,  83 

Fillers  for  joints,  99 

Fills,  see  Embankments 

Finishing  concrete  surfaces,  102 

Flash  point  of  oils,  114 

Float  test  of  bitumens,  125 


Florida,  funds  for  roads,  193 

motor  cars,  195 

road  mileage,  192,  194 
Fluxes,  116,  123 
Fords,  36 

Forms  for  concrete  roads,  99 
Foundations,  brick  roads,  163 

bridges,  35 

concrete  roads,  90 

culverts,  33 

gravel  roads,  67,  60 

macadam  roads,  68 

on  sand,  55 

steep  grades,  20 

telford,  27,  68 

French  coefficient  of  wear,  86 
Funds  for  road  work  in  the  different  Stated,  193 

Gabbro,  75,  87 

properties,  78 
Garnet,  83 
Georgia,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Gilsonite,  122 
Glutrin,  62,  72 
Gneiss,  75,  88 

properties,  82 
Grade  crossings,  9 
Graders,  40 

elevating,  42 

gravel  roads,  56,  58,  60 

sand-clay  road  uses,  49 
Grades,  1,  4,  11 

effect  on  traction,  4 

improved  by  relocation,  3 
Grading,  38,  40 

light  cuts  on  hard  roads,  5 
Giahamite,  123 
Granite,  75,  87 

properties,  79 
Gravel  bed,  57 
Gravel,  crushing,  54 

for  concrete  roads,  94 

length  of  road  which  a  load  of  gravel  of 
given  size  will  cover  to  given  loose  depths, 
61 

mechanical  analysis,  53 

production,  199 

quantity  of  loose  gravel  for  a  mile  of  road  of 
different  widths  and  thicknesses,  55 

quantity  required  to  give  different  depths 
when  lying  loose  on  a  mile  of  road  of 
different  widths,  55 

road-building  grades,  51, 57 

screening,  54,  59 

spreading,  61 

weight,  56,  62 
Gravel  roads,  51 
Gravel^asphalt  roads,  147 
Grout  joints  for  brick,  171 
Grubbing  right-of-way,  39 
Guard  rails,  25 
Gulfoilfield.llO 


Hardness,  test  for,  85,  121 
Harrowing,  bituminous  macadam,  141 

broken  stone  roads,  71 

gravel  roads,  56,  58 

Heating  binders  and  road  oils,  130,  142,  145 
Highway  maintenance,  see  Maintenance  of 

Roads 

Hillside  brick,  159 
Hornblende,  83 
Hydrocarbons,  109,  116 


INDEX 


211 


Idaho,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Illinois,  bituminous  roads,  141,  142,  144,  145 

brick  roads,  161,  167,  169,  178 

funds,  193 

gravel  roads,  52,  57 

motor  cars,  195 

oil  field,  110 

road  mileage,  192,  194 
Indiana,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Inorganic  matter  in  bitumen,  116 
Iowa,  automobile  accidents,  25 

funds  for  roads,  193 

motor  cars,  195 

road  mileage,  192,  194 

Joints,  brick  roads,  169,  171 

concrete  roads,  99 
Joint  fillers,  99,  175 

Kansas,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Kaolin,  84 
Kentucky,  funds,  193 

motor  cars,  195 

organization  for  road  dragging,  45 

road  mileage,  192,  194 

Layers  in  embankments,  39 
Lima-Indiana  oil  fields,  110 
Limestone,  84,  87 

properties,  79 
Loam,  absorption  and  retentivity,  20 

slopes  in  cuts  and  fills,  5 
Location  of  roads,  1 

at  grade  crossings,  10 
Loss  by  volatilization  of  oils,  114 
Louisiana,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 

Macadam  roads,  bituminous,  139 

water-bound,  64 

surface  treatment,  152 
Magnetite,  83 
Maine,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Maintenance,  bad  roads,  1 

bituminous  roads,  153 

concrete  roads,  104 

dragging,  43 

earth  roads,  43 

gravel  roads,  62 

macadam  roads,  73 

sand-clay  roads,  50 
Malthenes.  116 
Manjak,  123 
Maps,  California  commission  regulations,  16 

Vermillion  County  improvements,  4 
Maracaibo  asphalt,  122 
Marble,  75,  88 

properties,  81 
Marshes,  roads  across,  21 
Maryland,  bituminous  concrete,  145 

brick  roads,  175 

funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Massachusetts,  bituminous  roads,  140, 144 

funds,  193 

gravel-asphalt  roads,  147 


Massachusetts,  motor  cars,  195 

road  mileage,  192,  194 
Mastic  joint  fillers,  174 
Mexican  asphalt,  119,  122 
Mica,  83 
Michigan,  funds,  193 

gravel  for  roads,  51 

motor  cars,  195 
Michigan,  road  mileage,  192,  194 

water-bound  macadam,  64 
Mid-continent  oil  fields,  110 
Mileage  of  roads,  192,  194 
Minerals  in  road  building  rocks,  83 
Minnesota,  funds,  193 

motor  cars,  195 

water-bound  macadam,  64 

road  mileage,  192,  194 
Mississippi,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Missouri,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 

Mixers  for  bituminous  concrete,  341,  391,  400 
Mixers  for  concrete,  97, 101 
Mohs,  scale  of  hardness,  83 
Monolithic  brick  roads,  167 
Montana,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Motor  trucks,  road  widths  needed  for,  7 
Muscovite,  83 


Nebraska,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Nevada,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
New  Hampshire,  funds,  193 

gravel  roads,  63 

motor  cars,  195 

road  mileage,  192,  194 
New  Jersey,  broken  stone  specification*,  98 

funds,  193 

gravel  for  roads,  51 

motor  cars,  195 

road  mileage,  192,  194 

telford  specifications,  68 
New  Mexico,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
New  York,  bituminous  roads,  141,  145 

brick  roads,  161 

funds,  193 

grade  crossing  regulations,  10 

motor  cars,  195 

road  mileage,  192,  194 

telford  specifications,  68 

water-bound  macadam,  64,  67,  153 
North  Carolina,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
North  Dakota,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Note-keeping  on  surveys,  12 
Nozzles  for  road  oil,  142 

Ohio,  bituminous  macadam,  141 
brick  roads,  161,  168,  173 
funds,  193 
macadam,  67 
motor  cars,  195 
road  mileage,  192,  194 


212 


INDEX 


Oiling  roads,  150 

gallons  of  bituminous  material  per  mile 
of  road  for  different  rates  of  application, 
140 

gravel,  63 

macadam,  74 
Oils,  classification,  109 

equivalent  volumes  at  different  tempera- 
tures, 131 

classification,  109 

road, 124, 135 

shipping,  128 

specific  gravity,  weight  and  volume  at  60°, 

129 
Oklahoma,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Oregon,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Orthoclase,  83 
Outlets,  ditches,  22,  26 

drains,  29 

Paraffin,  109,  116 

Patrol  system  of  maintenance,  297 
Penetration  roads,  126,  139 
Penetration  test  of  bitumens,  121 
Pennsylvania,  bituminous  roads,  141,  153 

brick  roads,  161,  167,  175 

funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Petroleum,  109 

specific   gravity,    degrees   Baume1,    weight 

and  volume  at  60°,  112, 129 
Pipe  culverts,  33 
Plagioclase,  83 
Plans,  Vermilion  C9unty  improvements,  4 

California  commission  regulations,  16 
Plowing,  in  grading,  38 

sub-grades,  60 

Ponding  concrete  roads,  96,  104 
Pouring  cans,  143 
Pumping  road  oil,  128 
Pyro-bitumens,  118 

Quartz,  83 
Quartzite,  88 
properties,  81 

Rattler  test,  160 

Refining  petroleum,  111 

Residuums,  114 

Resistance  of  roads  to  traction,  189 

Retentivity  of  clay,  loam,  etc.,  20 

Rhode  Island,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Rhyolite,  75,  87 

properties,  78 
Rights-of-way,  7 

clearing  and  grubbing,  41 
Road  machines  (graders),  40 
Roadbed,  elevation  for  drainage,  22;  grading, 

38,60 

Road  plane,  see  Dragging 
Roads,  asphalt  block,  148 

bituminous,  138 

brick,  157 

concrete,  90 

costs  per  mile  corresponding  to  different 
costs  per  square  yard,  70 

dragging,  44 

drainage,  19 

earth,  37 


Roads,  grade  crossings,  9 

grades,  4 

gravel,  51 

gravel-asphalt,  147 

location,  1 

macadam,  bituminous,  138 

water-bound,  64 

maintenance,  1,  43,  50,  62,  73,  104,  153 

mileage,  193, 195 

resistance  to  traction,  189 

sand-clay,  47 

sand-oil,  147 

sections,  6,  21 

semi-arid  regions,  46 

top-soil,  see  Sand-clay 

widths,  6,  21,  92 
Rock  crushing,  66 
Rock  for  roads,  see  Stone 
Rolling  roads,  earth,  43 

gravel,  58 

macadam,  bituminous,  62,  63,  146 

sand-clay,  49 

water-bound,  71,  72 
Runoff,  factors  influencing,  30 

Sand,  absorption  and  retentivity,  20 

for  concrete,  93 

for  cushion  for  brick,  166 

production  of  paving,  199 

slopes  in  cuts  and  fills,  5 

weight,  56 

Sand-asphalt  roads,  147 
Sand-clay  roads,  47 
Sandstone,  75,  87 

properties,  80 
Schist,  75,  84,  88 

properties,  82 
Scrapers  for  grading,  38 
Screening  gravel,  59 

rock,  67 

Seal  coats,  139,  144,  146 
Section-line  roads,  2 
Serial  bonds,  187 
Shale,  75,  88 
Shoulders,  gravel  roads,  58 

macadam  roads,  72 

concrete  roads,  92 

bituminous  roads,  142 
Shrinkage  of  embankments,  40 
Silt,  absorption  and  retentivity,  20 
Single-track  roads,  7,  92 
Sinking  fund  bonds,  185 
Slag,  89 
Slaking  clay,  47 

rock  powder,  85 
Slate,  75,  88 
Slopes  of  cuts  and  fills,  5 

protection,  26,  33 
South  Carolina,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
South  Dakota,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Specific  gravity  determinations  of  oil,  114 
Steam  shovels,  38, 
Stone,  crushed,  see  Rock 

length  of  road  which  a  load  of  stone  of  given 
size  will  cover  to  given  loose  depths ,  61 

production,  198 

quantity  required  to  give  different  depths 
when  lying  loose  on  a  mile  of  roadway  of 
different  widths,  55 

sizes,  67 

weight,  66 
Stone,  for  bituminous  roads,  138, 141, 144 


INDEX 


213 


Stone,  for  concrete  roads,  93,  96 

for  water-bound  macadam,  64 

mineral  composition,  75 

physical  properties  and  tests,  85 
Straight-run  bituminous  products,  133 
Streak  of  minerals,  121 
Sub-grades,  brick  roads,  163 

concrete  roads,  90 

gravel  roads,  60 

macadam  roads,  69 
Summits  in  ditches,  25 

on  roads,  5 
Surfacing  roads  with  bituminous  materials, 

150 

Surveys,  regulations  of  California  commis- 
sion, 12 
Swamp  roads,  21 

Talbot's  culvert  formula,  30 
Tar  and  tar  products,  132 
Telford  foundations,  27 
Tennessee,  funds,  193 

motor  cars,  195      / 

road  mileage,  192,  194 
Texas,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Tile  drains,  27 

Top  soil  roads,  see  Sand-clay  Roads 
Toughness,  test  for,  85 
Traction,  effect  of  grades,  4 

resistance  of  roads  to,  189 
Tractors,  41,  100 
Trap,  83,  84,  87 

Trench,  for  gravel  and  broken  stone,  57,  60,  69 
Trinidad  asphalt,  118 
Trumbull  process  of  refining  petroleum,  113 

Underdrains,  27 
for  embankments,  23 
size,  24 


Underpasses  on  New  York  highways,  10 
Utah,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 

V-drains,  27 
Vermont,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Vertical  curves,  5 
Virginia,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Viscosity  of  bitumens,  125 
Volatilization  test  of  oils,  114 

Wagons,  38 

spreader,  70 
Washington,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Water-bound  macadam  roads,  64 
Water-brakes,  25 
Water  for  concrete,  101 
Wear  of  rocks,  test,  86 
Weathering  of  rocks,  85 
Wentworth's  culvert  formula,  32 
West  Virginia,  funds,  193 

motor  cars,  195 

road  mileage,  192,  194 
Width  of  roads,  5,  92 

at  grade  crossings,  10 
Wisconsin,  funds,  193 

gravel  roads,  59 

motor  cars,  195 

road  mileage,  192,  194 

standard  road  sections,  5 

water-bound  macadam,  64,  67 
Wyoming,  funds,  193 

motor  cars,  195 

oil,  111 

road  mileage,  192, 194 


ANNOUNCEMENTS 


215 


INDEX  TO  ANNOUNCEMENTS 

Asphalts  and  Allied  Substances  by  Herbert  Abraham 226 

Asphalts  by  T.  H.  Boorman ...  220 

American  Ballast  Co 224 

Atlas  Portland  Cement  Co 218 

Barber  Asphalt  Paving  Co.,  The ...  217 

Barrett   Company,  The 219 

Boorman,  T.  Hugh 220 

Clark,  Edward  A 220 

Granite  Paving  Block  Manufacturers  Assn.  of  the  U.  S.  A.  Inc 222 

Hastings  Pavement  Co.  Inc.,  The 223 

Koehring  Machine  Co 225 

New  York  Mastic  Works 220 

Robeson  Process  Co 220 

Societa  Sicula  per  Pesplotazione  dell'  Asfalto  naturale  Siciliano. 224 

Spencer,  W.  B 220 

Union  Oil  Co.  of  California 220 

Van  Nostrand  Co.,  D 220,  226 

Willite  Road  Construction  Co.  of  America,  Inc. . .  .221 


21G 


The  Standard  of  Comparison 
for  Paving  and  Road  Materials 

To  claim  that  a  paving  or  road-building  material  is  as  good 
as  Trinidad  or  Bermudez  asphalt  is  considered  the  strongest 
endorsement  that  can  be  brought  forward. 

But  the  materials  for  which  this  claim  is  made  are  usually 
new  and  untried,  and  year  after  year  one  "Just-as-good-as- 
lake-asphalt"  follows  another  into  oblivion. 

Bermudez  Trinidad 

Road  Asphalt  Lake  Asphalt 

Meanwhile  the  use  of  the  lake  asphalts  steadily  increases, 
and  their  position  as  the  standard  materials  by  which  all 
others  are  judged  is  more  firmly  fixed  (1)  by  the  continued 
good  service  of  natural  asphalt  roads  and  pavements,  some 
of  which,  though  30  years  old,  are  in  service  today;  and  (2) 
by  the  duplication  of  unfortunate  experience  with  artificial 
or  manufactured  asphalt. 

Engineers  and  officials  with  reputations  to  preserve,  and 
taxpayers  whose  money  is  to  be  spent  may  well  consider  also 
that  even  if  there  was  any  material  for  paving  and  road- 
building  equaling  the  lake  asphalts  in  stability,  dependability 
and  long  life,  it  would  take  30  years  to  prove  it. 

THE  BARBER  ASPHALT  PAVING 
COMPANY 

PHILADELPHIA  PENNSYLVANIA 


217 


SEND  FOR  THIS  FREE  BOOK 


A  practical  BOOK  for  engineers,  contractors  and 
public  officials.  Obtain  your  copy  by  writing  the 
Service  Department  of 

The  Atlas  Portland  Cement  Company 

Member  of  Portland  Cement  Association 

30  Broad  St.,  New  York  Corn  Exchange  Bank  Bldg.,  Chicago 

Phila.     Boston     St.  Louis     Minneapolis     Des  Moines     Dayton     Savannah 


218 


The  Company 


Road  Materials,  Etc. 

The  Barrett  Company  has  a  record  of  forty  years  in  fur- 
nishing paving  materials.  Its  experience  and  reputation 
gained  through  the  years  are  coupled  with  progressiveness. 
Its  engineers  and  chemists  are  constantly  at  work  on  the 
solution  of  new  problems.  Each  year  marks  a  distinct 
advance. 

Barrett    materials    combine    knowledge   and   experience. 

"Tarvia-X"  is  used  as  a  binder  in  the  construction  of  mac- 
adam roads. 

"Tarvia-A"  and  "Tarvia-B"  are  used  for  maintenance  on 
many  kinds  of  roads. 

Barrett's  Paving  Pitch  is  used  as  a  filler  on  stone  block, 
wood  block  and  brick  paving.  Special  grades  are  made  to  meet 
every  requirement  and  a  new  mastic  filler  has  been  developed  for 
use  in  stone  and  brick  pavements. 

Barrett's  Carbosota  Creosote  Oil  is  designed  for  preserv- 
ing all  timber  used  in  highway  fences  and  bridges. 

Barrett's  Ever  jet  Paint  is  a  black  paint  designed  for  pro- 
tecting exposed  ironwork. 

Booklets  and  particulars  on  request 


The  Company 


New  York      Chicago      Philadelphia      Boston  St.  Louis      Cleveland 

Cincinnati  Pittsburgh  Detroit  Birmingham 

Kansas  City        Minneapolis        Salt  Lake  City        Seattle        Peoria 

THE  BARRETT  COMPANY,  LIMITED:  Montreal  Toronto  Winnipeg 

Vancouver  St.  John,  N.  B.  Halifax.  N.  S.  Sydney.  N.  S. 


219 


The  Literature  of 

ROAD  MAKING  and  MAINTENANCE 


On  our  shelves  is  the  most  complete  stock  of  technical,  industrial, 
engineering  and  scientific  books  in  the  United  States.  The  technical 
literature  of  every  trade  relating  to  road  work  is  well  represented, 
as  is  every  branch  of  Civil  Engineering. 

A  large  number  of  these  we  publish  and  for  an  ever  increasing 
number  we  are  the  sole  agents. 

ALL  OUR  INQUIRIES  ARE  CHEERFULLY  AND  CAREFULLY 

ANSWERED  AND  COMPLETE  CATALOGS  AS  WELL  AS 

SPECIAL  LISTS  ARE  SENT  FREE  ON  REQUEST 


D.  VAN  NOSTRAND  COMPANY 
PUBLISHERS  AND  BOOKSELLERS 


25  PARK  PLACE 


NEW  YORK 


UNION  OIL  COMPANY 
of  California 

ASPHALT— ROAD  OILS 

Los  Angeles  San  Francisco 

CALIFORNIA 


GLUTRIN  ROAD  BINDER 

Particulars  from 

ROBESON    PROCESS    CO. 

18  East  41st  Street 

New  York  City 

EDWARD  A.  CLARK 

Mining  and  Drilling  Engineer 

Asphalt,  Coal,  Manganese  and  Zinc  Properties 
for  Sale 

Park  Row  Building       New  York  City 


T.  HUGH  BOOKMAN,  C.  E. 

Consulting  Engineer 
Forti6cations  and  Military  Roads 
City  Pavements  and  Efficiency 
Washington  Building,  New  York  City 


W.  B.  SPENCER,  C.  E. 

SPECIALIST  IN 

ROAD   MACHINERY 


30  Church  Street 


New  York 


NEW  YORK  MASTIC  WORKS 

Established  1872 
Original  Importers  of   Neuchatel  and  Seyssel 

Rock  Asphalt 

War  and  Navy  Departments 

Specialists  in  Asphalt  construction 

T.  HUGH  BOORMAN,  Cons.  Eng. 

1  Broadway.  New  York  City 


ASPHALTS 

19t4  Road  Edition  by 
T.  HUGH  BOORMAN,  C.  E. 

Price,  $2.00 

W.    T.    COMSTOCK  CO. 
23  Warren  Street  New  York  City 


220 


How  to  Save  Transportation  Costs 

is  the 

Question  of  the  Hour 


Wl  LLITE 

TRADE     MARK     REG.     U.  S.     PAT.     OFFICE 


Pavement  for  Military  Roads 
and  Country  Highways 

Patented  U.  S.  A.,  July  11,  1916 

The  Invention  of  H.  P.  WILLIS,  B.E.,  M.  Am.  Soc.  C.  E.,  formerly 
Chief  Engineer  N.  Y.  State  Highway  Department 


Willite  has  the  overwhelming  commercial  advantage  over  all  other 
types  of  pavement  (which  have  to  pay  100  per  cent,  of  all  material  entering 
into  their  construction)  because  about  85  per  cent  of  all  the  raw  material 
(native  mineral  aggregate),  used  in  both  the  WILLITE  foundation  and 
WILLITE  wearing  course  costs  nothing,  as  it  is  obtained  right  in  the  road 
itself  or  adjacent  thereto.  This  filler  can  be  the  run  of  the  road  without 
selection,  no  matter  what  the  character  of  the  soil  may  be,  such  as  mixed 
earth,  sand,  gravel,  shale,  sedimentary  sand,  disintegrated  granite,  etc. 


Willite  Road  Construction  Co. 

of  America,  Inc. 
51  Chambers  Street  NEW  YORK 


221 


THE 


FIRST  COST 
ST  COST 


No  Waste 


Today's  Necessity 


State  Street,  Albany,  N.  Y. 


"I  believe  in  a  paving  programme  based 

on  future  needs.     I  use  Improved  Granite 

Block  Paving — once  down  no  more  worry." 

—The  Mayor. 

"I  am  for  Improved  Granjte  Block  Pav- 
ing every  time — it  gives  my  horses  a  good 
sure  footing  and  saves  delay." 

—The  Driver. 


Present  need  is  for  better  streets,  traffic 
has  never  made  such  demands  as  now. 

Make  your  streets  permanent,  eliminate 
repairing,  speed  up  transportation  in  your 
city,  make  it  safe. 

roved   Granite 
lock  Paving 

Longest  Life 

No  Repairs 

No   Maintenance 


"I  am  always  safe  from  skidding  and  my 
brakes  hold  on  Improved  Granite  Block 
Paving.  —The  Chauffeur. 

"I  am  first,  last  and  always  for  the  mayor 
or  the  official  who  puts  my  money  into 
Improved  Granite  Block  Paving.  Once 
down — down  forever." 

—The  Taxpayer. 


Good  Material  Well  Laid  is  Absolute  Economy 

Granite  Paving  Block  Manufacturers'  Ass'n 

of  the  U.  S.  A.,  Inc. 


31  State  Street 


Boston,  Mass. 


Facts ,  figures  and  practice 
of    best    engineers  A 

at  your    disposal  * 


Write  for^ 
our  Booklet 

PERMANENT   PAVING 

AND   LATEST 

SPECIFICATIONS 

FOR   LAYING 


222 


Asphalt  Blocks 

for 

Resurfacing   Country  Roads 


A    REAL    PAVEMENT    ON    A    REAL    COUNTRY    ROAD 

ALBANY  POST  ROAD,   TOWN  OF  MT.  PLEASANT,   N.  Y. 

LAID  1910 
Part  of  an  Eight  Mile  Stretch  of  Asphalt  Blocks 

The  Asphalt  Block  is  a  composition  of  Trinidad  "Lake"  Asphalt,  crushed  trap  rock 
and  inorganic  dust,  thoroughly  mixed  at  a  temperature  of  300°F.,  and  pressed  into 
block  form  by  hydraulic  presses  working  under  the  tremendous  pressure  of  240 
tons  per  block. 

The  manufacture  of  Asphalt  Blocks  is  now  a  national  industry  with  plants  in 
many  parts  of  the  country.  The  use  of  Asphalt  Blocks  has  reached  a  total  of 
over  fifteen  million  square  yards. 

Asphalt  Block  Pavements  are  Durable,  Reasonable  in  Cost,  Pleasing  in  Ap- 
pearance, not  Affected  by  Extremes  of  Temperature,  Noiseless  and  Sanitary. 

The  field  for  Asphalt  Blocks  is  by  no  means  limited  to  their  use  on  public  streets 
and  roadways.  They  are  used  extensively  for  the  wearing  surface  of  piers,  ware- 
houses, loading  platforms,  bridges  and  factory  floors. 

Asphalt  Blocks  have  stood  the  test  of   time 

For  further  information  address 

THE  HASTINGS  PAVEMENT  CO. 

25  BROAD  STREET  NEW  YORK  CITY 


ASPHALT  FILLER 

Asphaltic  Roadway  Gravel 
Roofing  Gravel 


(MASCOT) 


LIMESTONE 


AMERICAN  BALLAST  COMPANY 

12161-1219  Holston  National  Bank  Building 

KNOXVILLE  TENNESSEE 


Societa  Sicula  per  1'esplotazione  dell' 
Asfalto  naturale  Siciliano 

(Own  Mines  and  Works  at  Ragusa,  Sicily) 

HEAD  OFFICE  AT  PALERMO,  VIA  GIRGENTI  3 

Cable  Address,  Rotland,  Palermo.     A.  B.  C,  5th  Ed.,  Code  used 

Exportation  of 

SICILY  .NATURAL  ROCK  ASPHALT 
SICILY  ASPHALT  POWDER   IN  50  KILO  SACKS 
SICILY  ASPHALT  MASTIC  IN  25  KILO  BLOCKS 
COMPRESSED  SICILIAN  ROCK  ASPHALT  SLABS 

MANY  MILLIONS  OF  SQUARE  METRES  IN  BERLIN,  PARIS,  VIENNA 
BUCAREST,  GLASGOW;  CAIRO,  EGYPT,  AND  ATHENS,  ALSO  IN  MONTREAL 
(CANADA),  AND  IN  NEW  YORK,  PHILADELPHIA,  BOSTON,  NEW  ORLEANS 
AND  OTHER  ATLANTIC  PORTS  IN  THE  UNITED  STATES  HAVE  BEEN 
LAID  WITH  SUCCESS  SINCE  1888. 

T.  HUGH  BOOKMAN,  Consulting  Engineer 

1  Broadway,  New  York 


224 


225 


600  Pages        6x9        Cloth        Illustrated         Postpaid  $5.00 

ASPHALTS  AND 
ALLIED  SUBSTANCES 

Their  Occurrence,  Mode  of  Production, 
Uses  in  the  Arts  and  Methods  of  Testing 

By  HERBERT  ABRAHAM 

B.S.  of  Chemistry,  Member  A.C.S.,S.C.I.,A.S.T.M.,I.A.T.M. 


CONTENTS 


Part  I.     General  Considerations 

Historical  outline,  norrenclature   and  classi-  of  bitumens  and  pyrobitumens.     Annual  pro- 

fication  9f  bituminous  substances.    Chemistry  duction  of  asphalts,  asphaltites  and  asphalti- 

of  bituminous  substances.     Geology  and  origin  pyrobitumens. 

Part  II.     Semi-Solid  and  Solid  Native  Bituminous  Substances 

Methods  of  refining.  Mineral  waxes  (Ozoker-  mineral  matter.  Asphaltite  deposits  (Gilsonite 
ite,  Montan  Wax,  Hatchettite,  etc.)  Deposits  of  Glance  Pitch  and  Grahamite).  Asphaltic  pyro- 
natural  asphalts  occurring  in  a  fairly  pure  state.  bitumen  deposits  (Elaterite,  Wurtzilite,  Albert- 
Deposits  of  natural  asphalts  associated  with  ite  and  Impsonite).  Pyrobituminous  shales. 

Part  III.     Tars  and  Pitches 

Methods  of  producing  tars  and  pitches.   Wood-  and  water  gas  tars  and  pitches;  Paraffins  wax 

tar,  wood-tar  pitch  and  rosin  pitch;  Peat  and  and  wax  tailings ;  Petroleum  asphalts;   Wurtzi- 

lignite  tars  and  pitches;   Shale  tar  and  shale  lite    pitch;    Fatty-acid    pitches    and  ,  bone-tar 

tar  pitch;  coal  tar  and   coal-tar  pitch;  oil-gas  pitch. 

Part  IV.     Manufactured  Products  and  their  Uses 

Methods  of  blending.     Bituminous  dust-pre-  Bituminous  sheet  roofings  and  floor  coverings, 

ventatives.    Bituminous  road-surt'acings.    Bitu-  Asphalt  shingles.      Bituminous   waterprcofiing 

minous  fillers  for  stone  or  concrete  pavements.  membranes.    Asphalt  insulating  and  sheathing 

Sheet  asphalt  pavements.    Asphalt  block  pave-  papers.    Asphalt  plastic  compounds.     Bitumi- 

ments.     Impregnated  wood  block  pavements.  nous    waterproofing,    compounds    for  cement. 

Wood  preservatives.    Asphalt  mastic  flooring.  Asphalt  paints,  varnishes  and  japans. 

Part  V.     Methods  of  Testing 

Physicalcharacteristics  (color,  fracture  lustre,  Naphthalene,    Paraffine,    Saturated   hydrocar- 

streak,  specific  gravity,  viscosity,  hardness,  due-  bons,  Sulphonation  Residue,  Mineral  Matter, 

tility  and  tensile  strength  tests).     Heat    tests  Saponifiable  Constituents,  Unsapqnifiable  Mat- 

(fusing  point,  volatile  matter,  flash  point,  burn-  ter  and  Glycerol).   Analysis  of  Paving  Materials, 

ing  point,  fixed  carbon  and  distillation  tests).  Analysis  of  Asphalt  Plastic  Compositions,  etc. 

Solubility  tests  (in  carbon  bisulphide,  carbon  Analysis  of    Sheet    Roofings,   Shingles,    Mem- 

tetrachloride ,    petroleum    naphtha    and    other  branes,  etc.    Analysis  of  Asphalt  Paints,  Var- 

solvents).      Chemical    tests    (Water,    Carbon,  nishes  and  Japans. 
Hydrogen,    Sulphur,   Nitrogen,    Free  Carbon, 


D.  VAN  NOSTRAND  COMPANY 

PUBLISHERS  AND  BOOKSELLERS 
25  Park  Place  New  York 


226 


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